Merge branch 'bugfix/jschatz1/sidebar-fixes/02-18-16' into 'master'

Uses cross browser niceScroll to do scrolling on sidebar.

Fixes: #13544 

Firefox does not support `-webkit-scrollbar` and there is no alternative for FF. So for example Gmail falls back to no fancy scrollbar. Stuck with jQuery, which is a good solution, since we already use it. 

This also leaves the default scrollbar as is. 

![Screen_Shot_2016-02-18_at_11.02.26_AM](/uploads/1184f06b71a8d9097ef1e3450a0c0ab3/Screen_Shot_2016-02-18_at_11.02.26_AM.png)

Also fixes horz scroll issue: 

![Screen_Shot_2016-02-18_at_11.09.56_AM](/uploads/63e9a8e824cac69a2745dd4dd84d1dfb/Screen_Shot_2016-02-18_at_11.09.56_AM.png)

cc @creamzy @dzaporozhets 

See merge request !2873

app/assets/javascripts/issuable_context.js.coffee

@@ -15,3 +15,5 @@ class @IssuableContext
       block.find('.selectbox').show()
       block.find('.value').hide()
       block.find('.js-select2').select2("open")
+
+    $(".right-sidebar").niceScroll()

app/assets/stylesheets/framework/gitlab-theme.scss

@@ -117,20 +117,4 @@ body {
   &.ui_violet {
     @include gitlab-theme(#9988CC, $theme-violet, #443366, #332255);
   }
-}
-
-::-webkit-scrollbar{
-  width: 3px;
-}
-
-::-webkit-scrollbar-thumb{
-  background-color:$theme-charcoal; border-radius: 0;
-}
-
-::-webkit-scrollbar-thumb:hover{
-  background-color:$theme-charcoal;
-}
-
-::-webkit-scrollbar-track{
-  background-color:#FFF;
 }