[WIP] Add support for installing plugins & themes by uploading ZIP files

[LukeTowers]

This PR adds the ability to install plugins & themes from ZIP archives, either uploaded through the backend or via the plugin:install and theme:install commands.

Currently working:

• plugin:install plugin(s).zip - supports single plugin, single plugin nested, multiple plugins no authors, multiple authors, and an entire plugins directory

TODO:

• Support theme:install theme(s).zip - support single theme, multiple themes
• "Upload Plugin" installer GUI - support all sources currently supported in CLI, user uploads a zip folder and then the plugins are installed and migrated using the same process that handles installing multiple plugins from the marketplace right now
• "Upload Theme" installer GUI - support same sources as CLI, user uploads a zip folder and then the themes are installed
• Testing

Eventually this will also play into the work in #967 and our overall marketplace support in general.

Work in progress.