Simplify

[ryguasu]

Curious if you agree that removing the need for hidden state (in particular saved_tokens/selected_token_index) might be a good direction for jquery-tokeninput. My motivations were:

• Fix https://github.com/loopj/jquery-tokeninput/issues/303
• Make the control a little easier to understand/maintain.
• Stay backward compatible

The first commit from this branch (206fbaa503a98bd42d5f40e3c65ba462a8de9912) is the central one. The second (206fbaa5) is a followup in case the first is thought to create performance problems by recalculating the entire hidden_input.val() string each time there's a token operation.

Cheers, ryguasu