Allow specificying config on sync (allow multiple datasets in a directory)

[yuletide]

As a user with 3-5 datsets to tile all living in the same directory, I want to be able to run mtsds --sync --config=isochrones_low.config (which would then point to isochrones_low.recipe) to specify which one to update.

Currently I have to edit my recipe and config every time, or put everything in separate directories just for MTS.