Better names for playback types

Some modifications were made to let users change the playback types names. Moreover it's possible to set if some playback types are visible or not to users.

Refs #1142
Merge branch 'master' into Feature1142
Simplify playback types views/routes, keep only the absolute necessary

We don't need all actions and views for playback types, since this is just
a helper model to store data for recordings. The only thing we really need
is a way to set playback types as shown/hidden.
So kept the update action only and simplified the views to be more like the
way they are intended to be in the apps: a single view where an admin can
update the visibility of all playback types.

refs #1142
Fix migration to 2.0.0 and add it to spec:migrations
Remove BigbluebuttonPlaybackType#i18n_key from the db

We don't really need it on the database since it's not really necessary for
apps to configure it.
Made a new method BigbluebuttonPlaybackType#name that returns the localized
name of the playback type.

refs #1142
Review PlaybackTypesController and add tests for it

refs #1142
A few more tests for sync of playback types

refs #1142
Merge pull request #19 from mconf/Feature1142

Better names for playback types, refs #1142