Fixed issues introduced

[alfredsgenkins]

Following issues were discovered in this repository

1. Folder plugins may only contain plugins, which export an object, components, anything else can not be located here. Action: I will try adding more detailed message about that!.
2. Extensions can not enable themself - the enabled extension resoltion is recurive - from your application root we scan all enabled extensions up, so it is not reccomended to enable extension in the same extension. Action - I will try adding an warnign about that
3. For some reason, potentially for some babel-specific reason the following code: import React from "react"; and then React.Component did not function correctly. Use the import { Component } from "react"; instead. This is a bug, but I am not sure if I will be able to address it soon enough.
4. Finally and most importantly, the local modules can only by symlinked if their version in package.json starts with link: and you are using yarn or file: but then manual symlinking is needed (yarn link or npm link).