[DONE] An Anvil client-code REPL

[campopianoa]

Also see this FR which I believe is the same.

[DONE] Interactive Anvil

Along the way to a full debugger, something like command line python interactive mode could be helpful. Trying to build out/test out more complex app_tables queries without having to run the application over and over would be productivity enhancing.

I may merge these at some point.