Extend DDPlanarDigi with an efficiency emulator

[BrieucF]

It would be super useful to extend DDPlanarDigi with a way to emulate hit efficiency. A first very simple approach could be to add user defined parameter(s) to set the desired efficiency (default to 1.), shoot for every simHit a uniform[0, 1] number and digitize this hit only if the random number is smaller than the efficiency parameter. What do you think?

Tagging @mahmoudali2 for the discussion as well.