configure quick access camera settings

[carandraug]

On #810 we removed the readout mode and gain setting from the camera panel on the main windows. The reason is that for most cameras that is no longer reasonable. We can see and change any setting via the settings button but there's too many there and not always visible. We would like to have a subset of them always visible and easy to change.

The proposal is that somewhere on a config file (possibly depot.conf) we list which of settings (in the camera settings dict) should be visible on the main window camera panel.