Plugin Manager (CLI)

This addresses #455 in a command-line fashion (laying the foundation for doing it in the web interface, eventually -- and with your guys help, without requiring a restart of strider [or at least having it self-restart])

Later I wish to add `install` and `uninstall` but I want to pause here and submit the PR to get some feedback before going any further.

See related project https://github.com/Strider-CD/strider-plugins for where "list remote" is getting its data.

Please note an ulterior motive here to move away from npm-based plugin management and towards a git-oriented one where the `strider-plugins` project maintains a canon for plugin and their stability, compatibility, and whatever other metadata in an easy to contribute way (npm permissions are a bitch, and there are too many strider-* projects on npm with no source code links, etc... i want to stop that and keep it 100% open. too many issues with people doing npm-update and being told to blow away their node-modules durectiry.... id rather we use git end to end for all plugin management.).

Looking forward to feedback and guidance
oh ok. Is there some standard file format we can conform to instead of making our own? not a huge thing, just a thought