javadoc, minor refactoring and renaming
comments
rename state0 to s0 for consistency
replace local variable with s0.getNonTransitMode()

it's just a getter method
reduce number of parameters to getNextTrip

We pass the entire state into the method, so time and on-street mode can
be fetched as needed from the state.
remove MASK_PICKUP/DROPOFF checks, should no longer be necessary

masked edges are not even created anymore.
move wheelchair-accessible check out from pattern to edge method

note: the getNextTrip wrapper function in TableTripPattern is now just a
timetable resolver, and can be renamed accordingly.
comment
eliminate getNextTrip wrapper from TableTripPattern

resolve timetable in board/alight traverse method
Initial commit of new index API