Generator: scripted process to upgrade Auro Custom Element

[blackfalcon]

Is your feature request related to a problem? Please describe.

Components can easily get out of step with the latest version of the generator. Fact, most of an element's project resources are for supporting the DX of the element. The core parts of the CE are on the ./src, ./test, and ./demo dirs.

There needs to be a way for a user to migrate these core CE files into a fresh install.

Describe the solution you'd like

A script that can run in the command line that will 'install' a new version of the WC-Generator into the scope of an existing element repo.

[blackfalcon]

The solution is to provide a simple shell script that can be downloaded and installed for use from the CLI.

See https://github.com/AlaskaAirlines/WC-Generator/blob/master/util/auroUpgrade.md for instructions.