Big change to calendar view functions. We now declare

Big change to calendar view functions.  We now declare
lower and upper bounds before loading calendar items into memory, so that the rendering code
doesn't have to go through thousands of recurrences that span way into the future.  Right now
it only uses this data to know when to stop iterating recurrences, but it could be fine tuned
even more to totally not store calendar items that are out of scope.