Module metadata file

A metadata file is a json file placed adjacent to a module jar file, with the same name as the module jar file but a .json extension. It is a copy of the module object in its repository, with a number of changes:

• No versions array
• New downloaded_version key. This is element from the versions array.

Moda needs metadata to display accurate descriptions, version and build numbers, and other important metadata in the "switchboard" GUI.