Add js milestone class. Activate drag-drop for issues on milestone page

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

app/assets/javascripts/dispatcher.js.coffee

@@ -21,6 +21,8 @@ class Dispatcher
         Issues.init()
       when 'projects:issues:show'
         new Issue()
+      when 'projects:milestones:show'
+        new Milestone()
       when 'projects:issues:new', 'projects:merge_requests:new'
         GitLab.GfmAutoComplete.setup()
       when 'dashboard:show'

app/assets/javascripts/milestone.js.coffee

@@ -0,0 +1,40 @@
+class Milestone
+  @updateIssue: (li, issue_url, data) ->
+    $.ajax
+      type: "PUT"
+      url: issue_url
+      data: data
+      success: (data) ->
+        if data.saved == true
+          $(li).effect 'highlight'
+        else
+          new Flash("Issue update failed", 'alert')
+      dataType: "json"
+
+  constructor: ->
+    @bindSorting()
+
+  bindSorting: ->
+    $("#issues-list-unassigned, #issues-list-ongoing, #issues-list-closed, #issues-list-reopened").sortable(
+      connectWith: ".issues-sortable-list",
+      dropOnEmpty: true,
+      receive: (event, ui) ->
+        new_state = $(this).data('state')
+        issue_id = ui.item.data('iid')
+        issue_url = ui.item.data('url')
+
+        data = switch new_state
+          when 'ongoing'
+            "issue[assignee_id]=" + gon.current_user_id
+          when 'unassigned'
+            "issue[assignee_id]="
+          when 'closed'
+            "issue[state_event]=close"
+          when 'reopened'
+            "issue[state_event]=reopen"
+
+        Milestone.updateIssue(ui.item, issue_url, data)
+
+    ).disableSelection()
+
+@Milestone = Milestone