(v4.1.0) Plugin.json improvements

[JasperAtSchool]

Plugin.json Improvements

• multiple authors: Allow multiple plugin authors & contributors.
  The old author(string) field should still work to keep backwards compatibility.
• versions: A list of compatible versions (e.g. OTv4.0.x, OTv4.1.x, OTv4.0.0, ODv1.0.0, ... the letters in the beginning specify the project: OT, OD, OM, OU)
• read before typecheck: read the plugin.json files from all plugins before doing the typescript compilation (index.js) & search for required npm dependencies.