Bug 961495 - [Task Manager] Opening transition

https://bugzilla.mozilla.org/show_bug.cgi?id=961495

This pull request makes it so that transitioning into the task manager from an open application will make it zoom out, onto the rocketbar. In addition to cleaning up the task manager, the following issues are solved here: 

* Keyboard is shown after dismissing task manager
* Tap or swipe should bring up task manager