Updated task.tpl; event.tpl; account.py; event.py; planner.py

Updates to task.tpl, event.tpl, and part of planner.py:
 - Add Task and Add Item forms now only display when the user has the permissions to add tasks and items to the event.
 - show_event and show_task now have a permissions check toward the end; the result is passed to the template. If the user doesn't have permissions to edit the event / task, then the forms to add a task or item do not show up.

Update to account.py:
 - Modified accountHasAdmin function to use the correct key when trying to retrieve the owner's username :-P

Update to event.py:
 - Added invUserToEvent
 - Fixed a small key string error in both addAdminToEvent and remAdminFromEvent.

Other update to planner.py:
 - Added /invUser view to handle form posts. Not yet sure how this is going to be implemented on the site, so didn't do the get view for this--easy to do if he need arises.