added Extension Point PAGES_PREPARED
added subPath concept for backend pages
simplified rex_be_controller
allow relative paths for subPath
set subPath automatically for plugin pages
added method rex_be_page::setSubPages()
Merge branch 'refs/heads/master' into inject-subpages
use page objects for content subpages
simplified content edit page
fixed content/meta subpage
added docs
Merge branch 'refs/heads/inject-subpages'

Conflicts:
	redaxo/src/addons/structure/plugins/content/pages/content.php