Adds ability to create new task from context select window.

Pulled in from tk-multi-setcontext and provides identical functionality.

Adds new App setting: allow_task_creation

![screen shot 2013-06-30 at 12 56 00 pm](https://f.cloud.github.com/assets/502705/727572/0f965e4e-e1a6-11e2-8b24-3024b5d5c785.png)