(io): rework RealSense grabber
Description
Current RealSense grabber (modules/io/realsense/SScan.cpp) is somewhat not so well written and could be improved. The selector force us to choose a realsense camera and use Qt to find the name. All of this should be transparent and only use libRealSense, to be a bit more user friendly.
Furthermore, the code seems to be very slow, especially in debug mode. Using faster iterator (scheduled in #625 (closed)) should also improve the situation.
Proposal
Make ui a bit more user friendly, make it faster