* refactor IDetector to have built-in, n-dim ROI support
* add methods for implicit ROI handling (no distinction to be made on caller's side)
* add docu for ROI
* refactor CoordSystem classes to not use detector and its ROI related things internally,
  but at caller's side. This eases transition handled in issue #71 ("Further consolidate ICoordSystem")

last user of this has been ParticleDistribution, which was removed in the last commits

make loader part of realDataItem; allow native data reset; add unit tests; data loader: cache result; parsing; error handling; load/store