Allow mixin support to be more inclusive.

Work with class APIs too. This requires using the
init convention and adding the method to the tip
classes.
Refine transition from text to input in editable-inline.

Include minor renaming.
Add and integrate autoprefixer Grunt subtasks.
Fix editable-inline plugin's FOUC problem.

Harden toggleOriginalDisplay's logic.
Reorganize tests directory structure.

Simplify from a module-based structure.

Also clearly separate visual tests (for future
qUnit integration).
Add qUnit and initial core extension tests...

Note that we're using QUnit.config.autostart and
QUnit.start for RequireJS compat.