Rename columns

Blocking.created_by => created_by_id
Blocking.created_at => created_dt

Photo.small_content => thumbnail
Photo.large_content => data

ReservationOccurrence.start => start_dt
ReservationOccurrence.end => end_dt
ReservationOccurrence.is_sent => notification_sent

Reservation.created_at => created_dt
Reservation.created_by => created_by_id
Reservation.uses_video_conference => uses_vc
Reservation.needs_video_conference_setup => needs_vc_assistance
Reservation.needs_general_assistance => needs_assistance
Reservation.start_date => start_dt
Reservation.end_date => end_dt

NonBookablePeriod.start_date => start_dt
NonBookablePeriod.end_date => end_dt

Room.notification_for_start => notification_before_days