Better support for dynamic and important plugins

I identified a few issues related to the title:

- dynamic plugins are not added to the internal state, so things like `list`or `remove` don't work
- help text should make clear that `enable` and `disable` are for static plugins only and make a `start` and `stop` command for dynamic plugins
- - **OR** overload `enable` and `disable` for dynamic plugins to be their `start` and `stop`
- using `remove` should stop a dynamic plugin
- plugin authors need to be able to mark their plugin `important` in the manifest and coffee should support that

I can make pr's for these if you like, but i wanted to gather some feedback first.