study_time_since
New `study_time_since` database function from session history. Add `Lion.timezone`. Add `Lion.day_start`. Add `Lion.studied_today`. Made `Table.queries` an instance variable. Renamed the session channel types.
Add `LEQ` condition type. Ensure that batch updates don't fire with nothing to update. Add `cast_row` to `update_many` for handling typed `NULL`s.
Redesigned data and core systems to be public-capable.
