api/interfaces.md - Split apart REST. Add major sections on AuthX.

This generally reorganizes the explanation of the REST API. Among other changes:

• Split apart into separate, more targeted pages (ie "Authentication", "APIv3 REST", and "APIv4 REST")
• Add more detailed comparison of APIv3 REST end-points
• Add description of AuthX authentication

Some preview links:

• http://spades.undo.it:8008/api/interfaces/#rest
• http://spades.undo.it:8008/api/v3/rest/
• http://spades.undo.it:8008/framework/authx/

This includes a few hyperlinks that depend on sysadmin!311 (merged)