Overlapping task offsetting and bug fixes.

* Add overlapping task offsetting with utility function and a new
  un-persisted task property "offset".

* Remove separate "duration" in task element scope and just use
  "task.duration".

* Fix bug with task font not resizing.

* Fix bug with displayed duration not updating on resize by using a
  separate "$scope.durStr" string variable that gets updated on
  "task.duration" changes.

* Fix bug where google calendar selection not being loaded on log in.

* Add a few pixels of padding to ".timeline" element so that tasks can
  be dragged from backlog to bottom edge of timeline.