Add further identification methods ++

[jtanx]

• Added API version. The server can now be queried for this, plus what sensors and actuators are available.
• Some refactoring - FCGI_RejectJSON now requires a description to be provided.
• The dump function now forces a download via the content-disposition header.
• The sensor ids were out of order with respect to their names (+ one name was missing - the segfault)

Potential refactor todo: Calls to FCGI_RejectJSON/FCGI_RejectJSONEx are automatically logged along with the description (reason) - remove redundant logging in handler functions.

[jtanx]

Actually about the sensor dump thing missing points; it was ok before because it's a do-while loop instead of a while loop. (woops)