Bug 935260 - Rework cards view as TaskManager and Card/TaskCard classes. r=alive

* Implement and use transform method on AppWindow
* Implement unapplyStyle, move settings change observer to registerEvents
* Use rocketbar.enabled setting to toggle isRocketbar property; unit test same
* More unit tests for isRocketbar behavior, testing setActive, hide
* allowManualClosing property to allowSwipeToClose, get rid of unused inTimeCapture, lastInTimeCapture
* Move opacity, transition, scale constants to card prototype. Use card.applyStyle to avoid touching the element.style directly. Fix pointer-events so current card should always be clickable. Fix adjacent card positioning so they occupy the 25% at the edge
* Adding unit tests for AppWindow apply/unapplyStyle, enter/leaveTaskManager and transform methods
* Add unit tests for card.destroy and taskManager.closeApp
* Adjust swipe_to_previous_app in cards_view ui-tests to start swipe from center
* Avoid side-effects when returning early from taskManager.show() (bug 999658)
Merge pull request #18377 from sfoster/task-manager

Bug 935260 - Refactor cards view to be instantiable, enable new task-manager look/feel and behavior behind HAIDA=1 build flag. r=alive