Missing feature: a "self" selection should be locked

The selection locking feature was removed in version 4 so I went with a solution suggested on stack overflow - namely, as each selection tag is rendered add a custom class if it's the principle user.

Relevant posts:

• https://stackoverflow.com/questions/16564425/how-to-implement-select2-with-lock-selection/48111387#48111387
• https://jsfiddle.net/o3s3y42e/4/

closes: #14 (closed)