new option to allow disable token edit

added new option `allowEditing`, which defaults to `true`, as to not break any current implementations.

Setting this option to `false` will disable the edit of token on double click.
Update test.tokenfield.integration.js
Added enter test for allowEditing false

Added an extra test for pressing enter on active token with `allowEditing` set to `false`
Update bootstrap-tokenfield.js
Update test.tokenfield.integration.js
Fixed wording on test description

Changed the wording to be consistent with other tests
Update bootstrap-tokenfield.js
Merge pull request #73 from tmorehouse/master

New option to allow disable token edit