Move the camera out to its own so that everything else is board-
related, and then rename BOARD_ADAPTER.
At some point the flags should probably be moved out too, and they
can have the EDA_3D_SETTINGS name.
ADDED: Back annotation algorithm,
eeschema back annotation dialog
CHANGED: added some minor helper methods to SCH_REFERENCE_LIST and SCH_REFERENCE,
split SCH_REFERENCE_LIST::CheckAnnotation on 2 parts to reuse code