OC_Cache namespace changes and add UserCache to server container.

Refs #4863
Add legacy wrapper
Add interface for Session and add getter in server container.
Purge session from Request - and fix some styles
Still some session leftovers.
Add some docs to the sessions interface.
Merge pull request #4888 from owncloud/public_session

Public session
Use new emitter system
Merge branch 'appframework-master' into public_cache

Conflicts:
	lib/public/iservercontainer.php
	lib/server.php
Note to self: Test before pushing!!!
Note to self 2: Do as you preach. Test!
updating php docs
Merge pull request #4886 from owncloud/public_cache

Public cache etc.
Merge branch 'appframework-master' into vcategories_public

Conflicts:
	lib/server.php