* Rename JsonMessageLoader to ULSJsonMessageLoader
* Correct the return type of mw.uls.loadLocalization
Follow up: Ic39dec1c484982fb07edd167e83794c0b5f470ee
Change-Id: I13c64a5e89ac75be8a95d951658018a78534f466
ApiULSLocalization is still present since we have to provide live
language preview feature.
Moved the loading of json file to includes/JsonMessageLoader.php
Also moved all RL modules to includes folder.
Bug: 56509
Change-Id: Ic39dec1c484982fb07edd167e83794c0b5f470ee