AP_Camera/AP_Mount: send camera info and settings messages to GCS

[rmackay9]

This adds basic support for AP_Camera and AP_Mount to send CAMERA_INFORMATION and CAMERA_SETTINGS messages to the ground station. This is important for the QGC custom camera/gimbal interface development.

The support is "basic" because only two of the camera drivers fill in the message details to any useful extent:

• Siyi driver provides the vendor and model names, firmware version, capability flags, recording mode and zoom percentage (see testing image below)
• MAVLinkCamV2 fully provides the CAMERA_INFORMATION message details but does not provide CAMERA_SETTINGS

Still, this is useful because the GCS work is being tested using a Siyi A8 and a follow-up PR will add support to the other drivers.

A small drive-by change is also made to the Siyi driver to display the camera firmware version (previously it only displayed the gimbal firmware version)

This has been bench tested on real hardware (Siyi A8 + CubeOrange)

[peterbarker]

Looks like these suggestions are move of an "if you're in the neighborhood thing, except for the default values thing.

Thanks for the reivew, I've addressed these issues I think.

[peterbarker]

LGTM