Fixes and updates for media uploads in the new editor

This PR fixes https://github.com/wordpress-mobile/WordPress-iOS-Editor/issues/344 and contains an updated editor pod which fixes an issue with remote URLs on images not being updated.

/cc @diegoreymendez 
Since this method is not a getter or setter, we can switch to accessing the property rather than the ivar.

We should also set `self.failedMediaAlertView = nil;` at some point, or else this dialog will never show up more than once per editor.