refactor(activity): minor refactoring and tests.
fix(media): add styles for media preview action buttons
clear unused styles and images
get rid of custom.css file

remove unused styles from custom.css
copy used parts in other relevant files
make close button look consistent

+ modal close
+ pane close
+ view close
remove old avatar upload scripts
make topnav action buttons consistent
feat(analytics): add support for piwik tracking

SD-274