Help with readability by using module.exports and require rather than the MobileFrontend
provided mw.mobileFrontend module manager (and avoid adopting webpack at this time)
Replace usages of mw.mobileFrontend.require with local require and module.exports
(compatible with RL or Node implementation)
Changes:
* Notifications modules are merged into skins.minerva.scripts and initialised
via a client side check.
* new file overlayManager for exporting an overlayManager singleton
rather than being hidden inside resources/skins.minerva.scripts/init.js
* All M.define/M.requires swapped out for require where possible
The `define` method is now forbidden in the repo.
Bug: T212944
Change-Id: I44790dd3fc6fe42bb502d79c39c4081c223bf2b1
