Remove duplicate mixing in of Discourse.Presence

AdminEmailIndexController and AdminEmailPreviewDigestController explicitely mix in Discourse.Presence, but they extend base classes Discourse.Controller and Discourse.ObjectController that already mix in Discourse.Presence, so this explicit inclusion is redundant.
Added screencast.com to whitelist.rb

Adding onebox support to screencast.com could be useful.
remove unnecessary (empty) view class

Discourse.ApplicationView does not provide any functionality above what
already automatically happens via Ember's "convention over
configuration" behavior and is therefore redundant.
Merge pull request #1448 from velesin/remove_redundant_presence

Remove duplicate mixing in of Discourse.Presence
mobile: fixed quote control jump
make category's RSS feed actually order by topic.created_at
if we have not automatic assets, don't try deleting them
Merge pull request #1454 from awesomerobot/master

mobile: fixed quote control jump
Merge pull request #1455 from alxndr/category-rss-ordered-by-created_at

make category's RSS feed actually order by topic.created_at
Merge pull request #1452 from velesin/remove_application_view

remove unnecessary (empty) view class
Fixed russsian localization
Merge pull request #1456 from Krugloff/patch-1

Fixed russsian localization
Merge pull request #1449 from seblavoie/patch-1

Added screencast.com to whitelist.rb
Revert "remove unnecessary (empty) view class"

This reverts commit 58ba8a0e49f0ac875c1eddfff843d3fe1927340f.
Fix missing provider param message when using Persona
Merge branch 'master' of github.com:discourse/discourse
Show mobile view as default for nexus 7 tablet
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  Show mobile view as default for nexus 7 tablet
  Fix missing provider param message when using Persona
  Revert "remove unnecessary (empty) view class"
  Fixed russsian localization
  if we have not automatic assets, don't try deleting them
  make category's RSS feed actually order by topic.created_at
  mobile: fixed quote control jump
  remove unnecessary (empty) view class
  Added screencast.com to whitelist.rb
  Remove duplicate mixing in of Discourse.Presence