SE3 prototype - hopefully according to current structure concept

NOT READY FOR MERGE
- not complete
- not correct
- just to have something to discuss / (dis)agree on

New here : SO3 and T3 are seen as speceial cases of SE3 (subgroups) and therefore children!

(runs fine with non optimized but crashes currently with optimized code - no time to debug, right now)
Yes, that is the only conceptually new thing. Think of SE3 as the name for the action interface: what can one do with SO3? It is exactly the same as one can do with SE3 : apply it to 3 or four column vectors. Same for T3. T3 and SO3 are just special each in a restriction sense when compared to SE3 in who exactly they operate - but that is not an difference in interface. Maybe one should have a different name for the common interface? What about Isometry3? Or Iso3? (this is what it all is about - preserving the Euclidean metric = iso-metric).