Document Mosaic Plugins

[DavieReid]

Document each of the Mosaic Plugins and describe the role of plugins in Mosaic architecture.

Overview

1. Plugin Lifecycle
2. Plugin runner
3. Main Process vs Child Process
4. Plugins enabled by default (refs and aliases)
5. How to add a plugin to mosaic config?

Per Plugin How to configure them? What features to they provide? What frontmatter is used/added/updated by the plugin