Parallel acquisition and moves

Scanning now starts moving to the next scan site while the current image is saving - this should save a chunk of time. Joe has also optimised it to integrate the initial autofocus move into the site-to-site move, shaving off another second.

The major change here is that we acquire raw images (at 2x2 binned resolution) and process them manually. This avoids some of the strange colour artifacts we see in the preview, and allows us to more easily parallelise the saving.

The big drawback of this approach is that it's now tied in to a particular camera and video mode. In the future I should move that code into the camera Thing, such that it will work with any camera.