Convert jasmine tests to mocha/chai

Allows for stack traces when running with phantomjs and many more
assertion options.

Splits <select multiple> tests into a separate file.
Isolate directive's scope

Evaluates selectize option in the directive's parent scope. Fixes #1.
Two-way bind to ngModel

Reinitialize the Selectize on model changes if the view is out of sync.
Fixes #2.