Allow filtering all lists by location and track

[superlou]

Currently, we can only filter to a single location.

• [ ] Filter to keep sessions in a list of locations
• [ ] Filter to keep sessions in a list of tracks

[superlou]

For session-list and session-brief, you can now specify location and track filters like the following:

!session-list
data:data_sessions_now.json
filter-location: Video 1 (WECC 123), Video 2 (WECC 123)
filter-track: Guest

This example will show all sessions in the json file in Video 1 or Video 2 AND are in the Guest track. The filter options must exactly match (case-sensitive) the information in Guidebook.

The filters are optional, and if you don't specify a location or track filter, the session topic will show all sessions in the json file.