This makes the popups in the plugin (those for editing and creating comments, replies, the pipeline, etc) configurable. Users can change the default width, height, transparency, and border properties, and set overrides per popup.
This MR represents a major refactor of the Go codebase, as well as introducing tests for the handlers. The MR also introduces an endpoint to shutdown or restart the Go server, which may be useful for clients who want to refresh the state of the plugin after checking out branches. Finally, this MR adds a contributing document for users who want to make feature changes.
