Draft: TRD clusterfinder rewriting.

For viewing by @apuntke, @a.bercuci and @p.kaehler.

This is the current state of my work on TRD hitfinders.

The main thing to look at for now is CbmTrdModuleRecR::BuildClusters(). This is my suggestion for efficient building of clusters in 1D. Row merging was removed for now, as the original implementation doesn't work as intended (discussed with @a.bercuci), and should be added as a post-processing step.