Merge branch 'filter_icons_btn' into 'master'

Filter icons look like proper buttons

The filter icons (Push events, Merge events, Comments, Team) now have a border
that signifies they can be pushed. This not only keeps it in line with the rest
of the application buttons, but it makes it more obvious, especially for the
Merge events button with a checkbox icon.

Fixes #1993

See merge request !1576

app/assets/stylesheets/sections/events.scss

@@ -184,6 +184,12 @@
   }
 }
 
-.event_filter li a {
+.event_filter {
+  
+  li a {
     padding: 5px 10px;
+    background: rgba(0,0,0,0.045);
+    margin-left: 4px;
+  }
+
 }