Use 'type' when 'name' is not present in DEG / SEG references
Adapt tests to 'type' if not 'name' change
Also skip DEGs if their minnum == 0 and an error occurs (ugly hack)
Change 'fillMsg' input format to nested maps, eliminate 'SF' type

The SF type was redundant in the way it ended up being used, its fields
got merged into the SEG type.

Providing data in nested maps has the advantage that it is easier to
detect if no data for a subpart was provided and that this should thus
be left out. It also provides more structure to the provided data over
the concatenation of keys which was pretty ad-hoc.

This is an intermediate commit, tests still need to be adapted and fixed.
Make tests compile
Fix some test errors
Allow missing definitions for segments that are not required or have only values

The error messages are still messy. It would be better to indicate errors
with more structure than with strings anyway.
Fix test client