CLI: Allow a filename to be specified when start rattle from the command line

[gjwgit]

Description

Support:

$ rattle mydata.csv

To start up Rattle and to load the given dataset.

Also, on Linux for example we could publish rattle as a handler of csv files so:

$ open mydata.csv

would start up Rattle

Why

So that as a user I can explore a dataset from the command line.

Closing Criteria

Checklist for closing the issue:

• All tests pass
• Command line invocation with an initial dataset

Alternatives

Currently as a user I need to start up Rattle and then navigate to the file of interest.

Additional Context

This is relevant for each of

• Linux
• macOS
• Windows