No feedback when camera gets off

[Raffaella Traniello]

When the camera is turned accidentally off Stopmotion keeps capturing the last frame it got. The user gets no errors. S/he may not notice s/he is missing many frames.

Note the interface is made in a way so that it's quite likely you'll get the camera accidentally off.
For capturing you need to turn the camera on by clicking on the camera button.
The mouse pointer will stay over the camera button since you don't need it for capturing (you will likely use the space bar).
On laptops the spacebar is very close to the left mouse button of the touchpad.

User should have a feedback in the preview that the camera went off (e.g. no preview anymore).