Update the DB model

- Remove calendar_multiple_meetings
- Remove calendar_regional_meetings
- Rename meeting_region into meeting_location
Adjust front-end and back-end library for the DB model change

This changes the output of the API a little but calling the API should be backward
compatible.

Clean the UI that calls for the LoginForm while we no-longer need it.
Adjust the unit-tests for the new DB model
Add the alembic revision script to update the db to the new model used in the app
Add link to the API in the menu and fix small typo
Add an Approved and a Denied icons that will be used in the date check function
Add endpoint to check the availability of a calendar at the specified date/time
Rework and simplify the agenda_is_free_in_future method
When creating a meeting give the option to the user to check if the agenda is free
Add unit-test to check the method agenda_is_free_in_future
Handle case where the input provided is incorrect and return the error message to the user
Add the check for availability in the edit meeting page as well
When checking availability in the time/date for an existing meeting we need its identifier
Check that there is a recursion_frequency before using it in a mo operation
Merge pull request #72 from fedora-infra/dev040

Dev040