Potential fixes: Transit usage in PILATES

[zneedell]

Running list of ideas to improve sensitivity to transit service with ActivitySim/BEAM integration:

• [x] Go back to recording experienced trip in skims (while having the option to include non-chosen alternatives as well)
• [x] Use real rather than generalized times and costs
• [x] Go back to merging in non-selected plans (after fix in #3560)
• [ ] Allow for specification of transit mode in input plans (e.g. if plans say WLK_COM_WALK choose a commuter rail route if possible)
• [x] Fix representation of not-used BEAM modes in skims (e.g. don't let people choose express bus, toll routes) [requires change to PILATES]
• [x] Add buffer time for drive transit so we don't have as many missed trips