DetectorCascade is awkward to initialize

[danielvarga]

DetectorCascade.imageWidth/imgHeight/imgWidthStep initialization has to happen before DetectorCascade::init() calls, through writing into public members. Turning them into init() arguments would be cleaner software design IMHO. But what really made my missing initialization hard to spot was that this line was commented out:

https://github.com/gnebehay/OpenTLD/blob/master/src/libopentld/tld/DetectorCascade.cpp#L85