Continue the migration of mobile.startup to webpack.
= Acceptance criteria
[] Skin built via webpack and tested by node-qunit
[] OverlayManager built via webpack and tested by node-qunit
[] Overlay built via webpack and tested by node-qunit
[] LoadingOverlay built via webpack and tested by node-qunit
[] rlModuleLoader built via webpack and tested by node-qunit
Note: Adding additional test coverage is out of scope and will be added separately.
Note: If tests cannot be ported (similar to View.js) create tasks and leave them be. Only port the trivial tests.
= Sign off steps
[] Measure and record code coverage on [[ https://www.mediawiki.org/wiki/Reading/Web/Projects/Invest_in_the_MobileFrontend_%26_MinervaNeue_frontend_architecture/Progress?useskin=vector | the wiki page ]]