UI improvements

* Percentage calculation now excludes inappropriate/hidden/oversighted
* Amount of feedback with and without comments is displayed
* Improved the feedback page header information: more compact; only displays
  amount of posts and percentage of positive votes
* Removed the "Showing:" prefix in front of the list of filters
* A couple of new SVG icons (like the negative/positive/neutral smiley faces)
* A couple of CSS improvements

Change-Id: I977c2a4acbdc2135ed548da1c0c2005b99aa4871
Merge "UI improvements"