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 
That would work as well... I just thought that `ConcurrentConnectionMaximum` can sound a bit too generic. (raising the question "connections for what?")