2.3/feature psr streams

Progress

This completes #2610

### Any model that extends Entry can act as a Stream

* For example, the Profile model now extends Entry with the stream_slug and stream_namespace properties set.
* The Profile model will now automatically be formatted by field types and will inherit all the OOP goodness.
* It also can be called as a relation attribute of the User like $user->profile and will be returned formatted.
* No need to call getStreamFields() method.
* Model attributes are formatted by default so you can do $profile->foo_field to get it.
* You can also call the unformatted attributes from the model like $profile->getUnformattedValue('foo_field')
* Or get the plugin value like $profile->getPluginValue('bar_field')

Some progress with the new stuff for the user plugin.