#869 add fields for graphic and stylesheet files
#869 support replacing graphic and stylesheet on template edit
#869 handle no files edits
Closes #924. Another Devilish Bug Vanquished.
fix screen permission (don't show all screens in other section)

- change block based screen abilities to non-block ones
- use cancan to get accessible screens
only load accessible root feeds

let the database do the hard work
only load submittable feeds from database

- copy submission creation rules to custom feed submit action
- use new Feed submit action for loading feeds
enforce show permission on feed to see submissions
add some test and cleanup naming
display group owned screen in my screens
Merge remote-tracking branch 'origin/master' into fix-screen-visibility
show all feeds for admins
fix feed visibility

wrong auth call caused the read permission to be not checked, thus feeds were not correctly filtered
Merge branch 'refs/heads/fix-feed-visibility' into improvements

Conflicts:
	app/controllers/dashboard_controller.rb
Merge branch 'refs/heads/fix-screen-visibility' into improvements
removed code duplication
transform screen abilities for feeds to non-block based
remove unnecessary usage of Feed.all

+ added tests for feed abilities implications (Feed update => Feed show => Feed => index)
remove unnecessary Screen.all and auth!
Merge pull request #928 from simplysoft/fix-feed-visibility

Fix feed visibility