inserted piwik tracking code
Merge remote-tracking branch 'origin/stable' into stable

* origin/stable:
  Update documentation
  Add active form documentation
  Update docs with latest yiistrap changes
  Remove collapse from navbar because it needs to be fixed
  Fix page titles
  Update the widget documentation
  Fix project urls
  Refactor some texts in the documentation
  Add logo and some patterns
  Update form documentation and add favicon
  Update form documentation