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
show all feeds for admins
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 remote-tracking branch 'origin/master' into improvements
Merge pull request #932 from simplysoft/improvements

Ability Checking & Performance Improvements