Merge branch 'new-snippet-button-permissions' into 'master'

Update New Snippet buttons.

## What does this MR do?

No longer shows New Snippet button to users who aren't able to create a new snippet in the given context.

Also removes the plus icon from the New Snippet buttons, as they're no longer used in other creation buttons.

## Are there points in the code the reviewer needs to double check?

Make sure the snippets pages don't break or show the buttons to users who shouldn't have access to them.

## Why was this MR needed?

Users that weren't logged in would click the New Snippet button and get a 404 error. You would also get 404 errors from the New Snippet button on project snippets for projects you weren't able to create snippets for.

## What are the relevant issue numbers?

Fixes #14595.

## Screenshots (if relevant)

Before:

![before1](/uploads/2c222cd981332d30772054cefadafa28/before1.png)

![before2](/uploads/2734f8a84ae293b08dd982f2ed7da028/before2.png)

After:

![after1](/uploads/c84aa9aec17056095271b0f24c6e9b5b/after1.png)

![after2](/uploads/70fe37ad7be5054bf20439ca0a1f5ccc/after2.png)

![after3](/uploads/afcd435c211482e9df25cb8971f1e65e/after3.png)

![after4](/uploads/9eab87440aae4991b508373ff36e3c7a/after4.png)

![after5](/uploads/f5ec167cb3e1115d3b3a43bd5231bc60/after5.png)

![after6](/uploads/c774cbb1f9babe3382ff69af7060b9c5/after6.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !4998

CHANGELOG

@@ -31,6 +31,7 @@ v 8.10.0 (unreleased)
   - API: Expose shared groups for projects and shared projects for groups !5050 (Robert Schilling)
   - Add "Enabled Git access protocols" to Application Settings
   - Fix user creation with stronger minimum password requirements !4054 (nathan-pmt)
+  - Only show New Snippet button to users that can create snippets.
   - PipelinesFinder uses git cache data
   - Throttle the update of `project.pushes_since_gc` to 1 minute.
   - Check for conflicts with existing Project's wiki path when creating a new project.

app/views/explore/snippets/index.html.haml

@@ -10,7 +10,6 @@
   - if current_user
     .pull-right
       = link_to new_snippet_path, class: "btn btn-new", title: "New Snippet" do
-        = icon('plus')
         New Snippet
 
   .oneline

app/views/projects/snippets/_actions.html.haml

 .hidden-xs
+  - if can?(current_user, :create_project_snippet, @project)
     = link_to new_namespace_project_snippet_path(@project.namespace, @project), class: 'btn btn-grouped btn-create new-snippet-link', title: "New Snippet" do
-    = icon('plus')
       New Snippet
   - if can?(current_user, :update_project_snippet, @snippet)
     = link_to edit_namespace_project_snippet_path(@project.namespace, @project, @snippet), class: "btn btn-grouped snippable-edit" do
@@ -8,12 +8,14 @@
   - if can?(current_user, :update_project_snippet, @snippet)
     = link_to namespace_project_snippet_path(@project.namespace, @project, @snippet), method: :delete, data: { confirm: "Are you sure?" }, class: "btn btn-grouped btn-warning", title: 'Delete Snippet' do
       Delete
-.visible-xs-block.dropdown
+- if can?(current_user, :create_project_snippet, @project) || can?(current_user, :update_project_snippet, @snippet)
+  .visible-xs-block.dropdown
     %button.btn.btn-default.btn-block.append-bottom-0.prepend-top-5{ data: { toggle: "dropdown" } }
       Options
       %span.caret
     .dropdown-menu.dropdown-menu-full-width
       %ul
+        - if can?(current_user, :create_project_snippet, @project)
           %li
             = link_to new_namespace_project_snippet_path(@project.namespace, @project), title: "New Snippet" do
               New Snippet

app/views/projects/snippets/index.html.haml

@@ -2,8 +2,8 @@
 
 .row-content-block.top-block
   .pull-right
+    - if can?(current_user, :create_project_snippet, @project)
       = link_to new_namespace_project_snippet_path(@project.namespace, @project), class: "btn btn-new", title: "New Snippet" do
-      = icon('plus')
         New Snippet
 
   .oneline

app/views/snippets/_actions.html.haml

 .hidden-xs
+  - if current_user
     = link_to new_snippet_path, class: "btn btn-grouped btn-create new-snippet-link", title: "New Snippet" do
-    = icon('plus')
       New Snippet
   - if can?(current_user, :update_personal_snippet, @snippet)
     = link_to edit_snippet_path(@snippet), class: "btn btn-grouped snippable-edit" do
       Edit
   - if can?(current_user, :admin_personal_snippet, @snippet)
-    = link_to snippet_path(@snippet), method: :delete, data: { confirm: "Are you sure?" }, class: "btn btn-grouped btn-warning", title: 'Delete Snippet' do
+    = link_to snippet_path(@snippet), method: :delete, data: { confirm: "Are you sure?" }, class: "btn btn-grouped btn-danger", title: 'Delete Snippet' do
       Delete
-.visible-xs-block.dropdown
+- if current_user
+  .visible-xs-block.dropdown
     %button.btn.btn-default.btn-block.append-bottom-0.prepend-top-5{ data: { toggle: "dropdown" } }
       Options
       %span.caret