included debug properties
Ueye: use correct interface class
add PointGrey camera device
PointGrey: modify device properties to match new interface
PointGrey: add attributes packet_size and packet_delay
PointGrey: add framerate control

Use Interface object for attribute access
PointGrey: make _PointGreyCam variable global

This prevents the camera object from being garbage collected.
PointGrey: add attributes gain_range, exp_time_range, frame_rate_range

Also, add units to gain, exp_time and frame_rate attributes.