Remove Editor MapDB code path

[landonreed]

In previous versions of this software, application and GTFS data were stored with MapDB. The application data has since moved into MongoDB and the GTFS storage has moved into Postgres. There is still some MapDB-backed code that is in use (for handling GTFS feeds in GTFSPlusController), but most of it is dead now that there is no longer a use for migrating code out of a MapDB database into Mongo/Postgres. Because of this fact, we should consider cleaning out the unused legacy classes for MapDB, including the following packages:

• com.conveyal.datatools.editor.models
• com.conveyal.datatools.editor.datastore