refs #4223 mark does plugins as core plugins
Merge branch 'master' of github.com:piwik/piwik
Merge branch 'master' of github.com:piwik/piwik

Conflicts:
	core/Plugin/Manager.php
improved layout, better wording, link to defveloper page
Merge branch 'master' of github.com:piwik/piwik
open link in new page