allows pt interaction

[fredshone]

I wanted a quick way to check with elara if we are getting multimodal access to transit.

This makes a slight tweak to the mode count tools such that they can measure mode shares for destination activity "pt interaction".

eg:

[plan_handlers]
trip_activity_modes = {destination_activity_filters=["pt interaction"]}

this is maybe a bit of a hack because we generally don't consider pt interaction as an activity. The above tool will effectively be measuring "leg" modes.

For example, given plan:

home -bike-> pt interaction -bus-> pt interaction -train-> pt interaction -walk-> work -car->home

trip_activity_modes = {destination_activity_filters=["home"]} will count 1 trip (the return) with mode car

trip_activity_modes = {destination_activity_filters=["pt interaction"]} will count 3 "trips" (all on the out trip) with modes bike, bus, and train.

This is only the case when specifying pt interaction as the filter. In all other cases behaviour is the same.

If we don't like this then we can make a new handler eg InterchangeModes or something similar. But i prefer this to avoid even more code.