Properly size tasks based on stack size.

There were a few places we weren’t doing this correctly

* When a new task is created the bounds should be the stack bounds
if the task is resizeable and not in freeform mode.
* When resizing a stack each task in the stack should be resized
base on if it is resizable vs. using the top running activity in
the stack to determine if all the tasks should be resized.

Change-Id: If3448c5629313e7e7fb91ffe8506014f16ad72db