precompute bbox

[DIDONAX]

• fixes /map/initial: precompute bbox #1276
• depends on add bbox nigiri#314

[felixguendling]

if it's stored in nigiri::timetable it should be computed in init_finish.cc.

The name tt.bbox_ implies that it's a bounding box covering every stop/trip/shape of the timetable which is not true.

[DIDONAX]

if it's stored in nigiri::timetable it should be computed in init_finish.cc.

in this case, would it be better to rewrite the necessary part from tiles in nigiri (~ 15 lines of code), or move them permanently to the geo library since it's already included in nigiri as dependency?

[felixguendling]

I think they can be moved to geo.