AP_Camera: Relocate feedback messages.

Relocated feedback message content according to Mavlink libraries
(msg_camera_feedback).
Included camera_flags for future developments.
Hi @arthurbenemann,
 
Thanks for comment ;)

I known the problem you are saying. I am entering in github world and I still not feel very secure when I do some changes and public pull request. Below you can see modified mavlink_msg_camera_feedback file according to the AP_ Camera changes that I made above.

I have not included this file and his commit before because I was not sure if I should do another pull request for every file that affects another library or folder...

Please, of course feel free to make any changes you think appropriate. 

Sorry for the inconvenients.
Thanks for your time.

Cheers,
Dario.