Sharing: Framework for applications to automatically add shares

Created by: JosephKiranBabu

Complexity: 1 point

After the sharing application is implemented add internal method API so that other Plinth application will be able to automatically share some folder.

• Assumption: Adding a share functionality is already available. See #947 (closed).
• Make listing of shares, adding of shares and removing of shares into an internal API for other applications to consume. Transmission and Deluge need to use this API to automatically share the downloaded files. This may not be much but think of proper API.
• Document the API in the developer manual.