Merge branch 'project-dropdown-position-fix' into 'master'

Fixed project dropdown being overlapped by sidebar

## What does this MR do?

Changes the header expanded `padding` to `margin` to prevent the project dropdown from overlapping.

## What are the relevant issue numbers?

Closes #18410 

## Screenshots (if relevant)

![Screen_Shot_2016-06-10_at_10.38.00](/uploads/b569d6d4cbd126fd776cf849ebc1137d/Screen_Shot_2016-06-10_at_10.38.00.png)

See merge request !4583

app/assets/stylesheets/framework/header.scss

@@ -185,7 +185,7 @@ header {
   margin-left: 0;
 
   .header-content {
-    padding-left: $sidebar_width;
+    margin-left: $sidebar_width;
     transition-duration: .3s;
   }
 }