Update event.tpl

Checks for permissions before showing add a task form
Update task.tpl

Added a permissions check to make sure user has rights to add an item before the form is displayed.
Update account.py

I was using the wrong key to get the event owner's username. Fixed.
Update event.py

 - Added invUserToEvent
 - Fixed a small key string error in both addAdminToEvent and remAdminFromEvent.
Update planner.py

Edited show_event and show_task:

 - Added 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.
Merge pull request #54 from CKnotts/master

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