Should support active_area params of MLV

[Andrew Baldwin]

MLV is now being used as a container for intervalometer pictures, but the active_area params must be observed to ignore the OB regions of the frame.

Reported by @dmilligan

[Andrew Baldwin]

As of f011eb1470e1118b1f8599d0770b065051e0f6be, ActiveArea is now read and written correctly to CDNG files. This should make DNG export behaviour match mlv_dump.

ActiveArea is not yet used to crop the black borders for display and MOV export.

[Andrew Baldwin]

Implemented in 1.2