When editing meetings we should make sure they do not conflict w/ themselves

When editing meeting we check if the time slot is available or not. For recurring meeting
we check this in the future but we have to find a way to tell that they should not
conflict with the future occurence of themselves.

This is the goal of this commit.
When updating the meeting_date for the edit form, check the end of the recursivity date

We do not want to propose the user to edit a meeting on Aug 13 when the recursivity
is in fact ending on the 12.
Merge pull request #19 from fedora-infra/fix_edit_recurring

Fix edit recurring