Construct filename more automatically, based on optional params in the upload command

The filename could optionally be constructed more automatically, for example:

`/zeus-upload <scenario_id> <filename="auto"> <modlist=None> <mission_date=today/None> <zeus_name=author> <mission_name=None>`

Entering `<filename>` would disable all other fields (except modlist), otherwise filename would be `Zeus_<mission_date>_<zeus_name>_<mision_name>`