Blocked on: T158980

After having experimented with using a bundler in Page previews, We will use webpack to generate MobileFrontend's mobile.startup module.

This will

• reduce size of RL module
• Avoid unnecessary file loading in ResourceLoader
• Make it easier for us to port to a submodule in future if necessary
• Remove the need for unnecessary globals
• Use npm libraries
• Allow us to experiment/investigate using Es5/6, template compiling
• Prevent us from surfacing functions purely for testing purposes e.g. in Skin.js we expose getSectionId;

acceptance criteria

• Use webpack to generate a single JS file that is included by mobile.startup that includes all the existing JavaScript
• Templates and LESS files will continue to be loaded via ResourceLoader
• Use exports/imports where possible for exporting/importing rather than M.define/M.require
• There is fast isolated unit testing with npm run test:unit e.g. https://gerrit.wikimedia.org/r/#/c/282899/
• Integrate code coverage reports and fail job on coverage decrease
• The closures around every file should be unnecessary after these changes (RL wraps code so no global var leakages, and eslint protects against unused/undefined variables used)

e.g. we can remove the following pattern

( function ( M, $ ) {