Fixes #3624, add donation form w/ slider and link to paypal in multiple places including: after update, default superuser dashboard, feedback popup.

Notes:
  * Fixed css bug in updater language selector.


git-svn-id: http://dev.piwik.org/svn/trunk@7746 59fd770c-687e-43c8-a1e3-f5a4ff64c105