Provide user interface for managing extensions

[CharliePoole]

@CharliePoole commented on Sat Dec 12 2015

Users need a way to install extensions, enable and disable them and update them. This could be a separate program or a set of files that get edited.

This depends in part on #1133 which deals with the underlying mechanism for installing extensions.

Updated 18 Jan 2022 -

For the the current console runner, there seem to be three options for this...\

1. Additional conventional locations for storing extensions.
2. A command-line option or options for the runner itself
3. A separate install program

I have ordered the options from easiest to hardest to implement at least at first glance. :-)