Remove unused, commented out CSS.

See #4102
Fix post settings menu cog alignment and colours
SERP style updates
Fix padding on content preview mobile views
Minor start on CSS Style cleanup

See #4107
Mobile bug fixes for users view
Fix overly tiny text
Fix broken link, remove old html files
Remove about page header on desktop

See #4116
Merge pull request #4118 from JohnONolan/053-fixes