Don't swallow error on startup

Startup errors which could point to the actual failure
were being swallowed by Blitz. NB: This particular error
condition was initially related to the Ice.IPv6 setting.

See:
* https://www.openmicroscopy.org/community/viewtopic.php?f=5&t=7527
* https://www.openmicroscopy.org/community/viewtopic.php?f=5&t=7456&p=14166#p14166
Introduce an optional IPv6=0 property

While we're at it, might as well place
an anchor in templates.xml so users can
more quickly find the formatting needed
to disable IPv6.
Fix typo in error message
Increase logging
Initial fix for unparsed metadata (See #12358)

This is only a band-aid over the issue of
table values being possibly non-scalar. Either
we will need to provide a getter that flattens
all values, or agree upon some API such as
DVExtHdrFields extending java.util.Map to make
this tractable.
Strip reference to DVExtHdrFields
Remove import and add main tester
Support RFloat from ModelMapper
Improve templates.xml explanation
Merge pull request #2689 from joshmoore/ipv6-error

Don't swallow error on startup
Merge pull request #2695 from joshmoore/rebased/dev_5_0/12358-parse-metadata

12358 parse metadata (rebased onto dev_5_0)