Swap out Chosen for Select2

[danielbachhuber]

• Replace Chosen with Select2.
• Update js/fieldmanager-select.js to do whatever is needed for updating Select2
• If AJAX data source is provided, use that.

See #244

[danielbachhuber]

Ugh. Select2 doesn't support ajax datasources for <select>.

Open to suggestions on which direction I should head.

[kevin-brown]

Ugh. Select2 doesn't support ajax datasources for <select>.

Might as well mention that as of 4.0.0, this is supported (and is the recommended default)

[danielbachhuber]

We'll consider Select2 for Fieldmanager 2.0.0, but not going to change things for 1.0.0