Autoexposure mode

[Raphael-Boichot]

Mode 1, active at boot: autoexposure with gain and exposure time (fast exposure time and high gain have priority to avoid blurry images) with some forced registers (some slight edge enhancement, some standard voltages) to mimic the original rom behavior.
Mode 2: lock the current settings as they are and allows modification by hand of all registers.
SELECT to shift between the modes.

[HerrZatacke]

Requires #13

[HerrZatacke]

Preferrabls two options:

• priority exposure
• priority gain.