Address early AM bugs

[PaulJKim]

Summary of changes

Asana Ticket: Implement early AM prediction changes

While observing early AM predictions play out with Kevin and Jim, we spotted two bugs.

The first was that the Prudential MZ sign was filtering out reverse E branch predictions. This is because the filtering logic was using sign_ids to exempt Prudential and Symphony EB. Now, the logic uses stop_ids so Prudential's MZ EB line will now also be included in the filtering logic. This required an additional change to pass the stop_id to StoppedTrain messages so that the filtering logic could access it.

The second bug was one where the second line of MZ headway messages was sometimes getting cut off. This was because one of the lines was exiting the early AM state and therefore just passing along half of the headway message from the original content generation logic. To resolve this, the logic now will put the original headway message back together if the line has early AM state :none so that the proceeding logic will have both lines to work with.

While not related to early AM logic, there was also a minor config issue that we noticed during the observation as well where the Kenmore B platforms were using the green_trunk headway group. It's preferable for these platforms to use the green_b headway values so that we don't say that trains are coming more frequently than they are on the B branch platforms. There's also no reason the Kenmore WB B branch platform can't use the Boston Col headsign.

[panentheos]

Looks good.