Add plugin package manager

[johnmaguire]

I'm envisioning the ability to PM Cardinal with plugin search <term>, and getting back a list of packages matching the term.

The commands I can think of that would be most important:

plugin search <term>
plugin install <package>
plugin uninstall <package>
plugin info <package>

Probably loading / unloading / etc. of plugins would get off-loaded to this package.

I just bought the domain http://getcardinal.org, so an API for searching the "repository" could be hosted there.

[johnmaguire]

Some other thoughts I've had: Searching system-wide for packages beginning cardinal-plugin-. This would allow you to pip install plugins and have them available. It would be cool to have the ability to install Cardinal globally through pip (and keep it updated that way), while also being able to maintain system-wide plugins through pip. While not necessarily 100% best practice, it makes Cardinal a little more convenient for casual users.

[johnmaguire]

https://stackoverflow.com/questions/7492855/getting-an-embedded-python-runtime-to-use-the-current-active-virtualenv

It looks like virtualenv comes with a bin/activate_this.py. Theoretically, each plugin could get its own virtualenv, and install dependencies locally. 👍