Merge branch '23147-file-viewer-header-has-hover-style' into 'master'

Improved specificity of toggleable file headers

## What does this MR do?

Improves the specificity of the diff file title toggle styling.

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

## Why was this MR needed?

Currently, any `.file-title` will have a pointer cursor and background colour change on hover. This should be only for diff files, except discussion diff files.

## Screenshots (if relevant)

![2016-10-14_13.57.12](/uploads/e8561bed378487b8d14d579ce31417d0/2016-10-14_13.57.12.gif)![2016-10-14_14.01.15](/uploads/e88858874377fa83aa5e632ec9e1a601/2016-10-14_14.01.15.gif)![2016-10-14_14.01.46](/uploads/8a773ee6bb29386f2dc022bb2ffaf474/2016-10-14_14.01.46.gif)

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?


Closes #23147

See merge request !6887

app/assets/stylesheets/framework/files.scss

@@ -26,15 +26,6 @@
     padding: 10px $gl-padding;
     word-wrap: break-word;
     border-radius: 3px 3px 0 0;
-    cursor: pointer;
-
-    &:hover {
-      background-color: $dark-background-color;
-    }
-
-    .diff-toggle-caret {
-      padding-right: 6px; 
-    }
 
     &.file-title-clear {
       padding-left: 0;

app/assets/stylesheets/pages/diff.scss

@@ -33,6 +33,19 @@
       font-size: smaller;
     }
   }
+
+  .file-title {
+    cursor: pointer;
+
+    &:hover {
+      background-color: $dark-background-color;
+    }
+
+    .diff-toggle-caret {
+      padding-right: 6px;
+    }
+  }
+
   .diff-content {
     overflow: auto;
     overflow-y: hidden;

app/assets/stylesheets/pages/notes.scss

@@ -147,6 +147,14 @@ ul.notes {
 
 // Diff code in discussion view
 .discussion-body .diff-file {
+  .file-title {
+    cursor: default;
+
+    &:hover {
+      background-color: $gray-light;
+    }
+  }
+
   .diff-header > span {
     margin-right: 10px;
   }