Move site ID into JSON file for em27-prep-i2s? #2

Might make sense to have the site ID be in the common args for em27-prep-i2s that can be passed as a JSON file, rather than always having to be a command line argument. My original thinking about the command line argument was that it might be useful if we have a location/met database and need the site ID to determine which entry to read. Now it seems like a site ID is a static thing that should be kept with the other static information.

I'll need to look a little bit into how v1 EGI handles locations and the like to see whether specifying the site ID to determine other inputs makes sense or not. It might also be that I create other subcommands which have the site ID as an input that automagically sets everything else.