Resetting previous shot when leaving walk mode.

Resetting previous shot since moving back and forth between moving modes using the same camera causes no images to be shown in walk mode from the second time and onwards.
Avoiding unnecessary overwrite of old image plane camera.

When moving between orbit and walk mode and selecting the same camera twice the old image plane camera will get overwritten with the new one causing a duplicated image plane. This is avoided by comparing the image plane with the new camera object.
Merge pull request #9 from oscarlorentzon/feature/moving-mode-transitions

Moving mode transition improvements