Add field cfp_type and relevant validations
Add Program#cfp to preserve backwards compatibility
Add 'for_events' scope to the cfp, in order for it to be used like
program.cfps.events
Add useful methods
Add rspec test for the new code
The supported cfp types can be viewed via Cfp::TYPES
The cfp_open? method uses Date.current, so it should also be tested with
Date.current and not Date.today
Also, build was replaced with create to fix a false negative
This is a partial fix for #1522
Also, the part of the schedule event is deleted and the length of the event types
changes to the nearest suitable after changing the length of the interval.
This closes#1220
