new feature: Camera Match

Camera Match creates a camera based on a image using vanish points.
Camera Match - fixed film back size

Film back size now calculated with the aspect ration of the backdrop
image. -> Focal length is now correct.
Camera Match - Angle of View fix
Camera Match - Error Messages and UI refinement

Implemented proper error messages for the user.
User now gets warned if:
- no image is loaded
- first or second vanish point is missing

Create Camera:
- view switches now to the new camera
- backdrop mode is changed to “camera”
- render resolution is now set to the loaded image

Some naming changes in the UI:
- X and Y-Axis renamed to “first vanish point” and “second vanish point”
- Help link now points to github wiki page
Camera Match - new feature & code clean up

- camera rotation can now be locked
- mesh for orientation is now deleted after camera is solved
- code clean up
Merge branch 'CameraMatch'

Conflicts:
	configs/CameraMatch.cfg
	scripts/CameraMatch.py