Switch between '.' and '_' separators in Schema, depending on version.
Remove workaround in centroid and shape slot definers.

Now that SubSchema works properly for version 1 tables, we can use it when
defining slots.  Also moved the implementation of the slot definers to the .cc file,
and fixed name used for point covariance terms (previously incorrect in both the
test code and the old implementation).
Reorder methods in Schema implementation to improve readability
Merge branch 'u/jbosch/DM-1058'