Adds method verification for interval overlap, tests, creates the migration. BUT NOT WORKING YET.
Ensures no colision or overlap in appointment creation.
Fixes tests. Implements interval between appointments.
Merge branch 'feature/appointment_interval' into develop

Conflicts:
	app/models/appointment.rb
	db/migrate/20140805012958_add_interval_to_service.rb
	db/schema.rb