[FEATURE] Add ReactPy and ReactJS app scaffold options to tethys quickstart

[shawncrawley]

Is your feature request related to a problem? Please describe.
The problem is that currently the tethys quickstart, which scaffolds a "Hello World" app for the user, is only currently able to do so in the standard app scaffold. It would be nice to do a quickstart using the ReactPy or ReactJS app scaffold, if desired.

Describe the solution you'd like
This could be achieved by adding an optional positional argument, like so: tethys quickstart [reactpy | reactjs]

Describe alternatives you've considered
The alternative is to only allow ReactPy and ReactJS apps to be scaffolded as a fresh, manual app scaffold, which is currently the case.

Additional context
None that I'm aware of.

[swainn]

Remove scaffolding from the quickstart in favor of GUI scaffolding. See #1145