ADHI-4769: Add support for dynamically labelled axes

This patch adds support for merging of histograms with dynamically labelled axes.

Dynamic labels mean one or more bins are labelled and followed by zero or more non-labelled, the ordering of labels can be arbitrary. When merging these axes we do remapping of bins and also strip non-labelled bins. When stripping we also check that those bins have no contents and issue a warning if bins are not empty. Some dynamic labels can look the same as static labels (if they have the same labels in the same order), for those we do a regular merge and don't strip non-labelled bins.

Fixes ADHI-4769.