Set initial value to Issue/MR form -> assignee selectbox

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/views/projects/issues/_form.html.haml

@@ -24,7 +24,7 @@
           %i.icon-user
           Assign to
         .col-sm-10
-          = project_users_select_tag('issue[assignee_id]', placeholder: 'Select a user', class: 'custom-form-control')
+          = project_users_select_tag('issue[assignee_id]', placeholder: 'Select a user', class: 'custom-form-control', selected: @issue.assignee_id)
            
           = link_to 'Assign to me', '#', class: 'btn btn-small assign-to-me-link'
     .form-group

app/views/projects/issues/_issue_context.html.haml

@@ -6,7 +6,8 @@
   - if can?(current_user, :modify_issue, @issue)
     = link_to profile_path(issue.assignee) do
       = image_tag(avatar_icon(issue.assignee.email), class: 'avatar avatar-inline s16 assignee') if issue.assignee
-    = f.select(:assignee_id, assignee_options(@issue), { include_blank: "Assign to user (none):" }, {class: 'select2'})
+
+    = project_users_select_tag('issue[assignee_id]', placeholder: 'Select a user', class: 'custom-form-control', selected: @issue.assignee_id)
   - elsif issue.assignee
     = link_to_member(@project, @issue.assignee)
 

app/views/projects/merge_requests/_form.html.haml

@@ -50,7 +50,7 @@
           %i.icon-user
           Assign to
         .col-sm-10
-          = project_users_select_tag('merge_request[assignee_id]', placeholder: 'Select a user', class: 'custom-form-control')
+          = project_users_select_tag('merge_request[assignee_id]', placeholder: 'Select a user', class: 'custom-form-control', selected: @merge_request.assignee_id)
            
           = link_to 'Assign to me', '#', class: 'btn btn-small assign-to-me-link'
     .form-group