ResourceLoader/V2 Task management

Main tracking bug: 29272

Before

 * Send out email about removing non-RL gadget support
 * Remove non-RL gadget support in advance of Gadgets 2.0 deployment

Meta todo

 * Create todo list
 * Send out email to recruit people to do work
 * Figure out when this will all be done

Actual work todo

 * Set up labs wiki ✅ - http://gadgets.wmflabs.org/
 * Support redirects for .js/.css pages (for future redirects from old MW: pages to migrated gadgets) - 71200, 71201
 * Metadata field in gadget definition for minimum MW version

Communication

 * Start talking to comms people about roll-out
 * Roll-out includes restricting gadget editing to new gadget editors group (which includes management rights as well)
 * Bureaucrats can grant locally; global editinterface group gets rights for global gadgets and local gadgets on each wiki
 * Longer term, we're going to remove MediaWiki:Common.js/css in the future in favor of (hidden) gadgets

Enhancements

 * Re-write gadget manager JS interface in OOJS
 * Add Special:Gadgets/gadgetname/tests or whatever that hosts a qunit runner