Refactor DAO by merging all filter parameters

[laurentg]

Currently various getter on the DAO layer accept different parameters to filter on different objects, for example:

trips = dao.trips(fltr=..., stop_fltr=...)

Merge the various filter into one, such as this:

trips = dao.trips(fltr=...)

That would need to be able to automatically join the appropriate table when needed (for example on table trip, joint stop_times then stops if we filter on stops).

[laurentg]

Fixed in 02cccde and 32ff3e4.