Import and validation fixups

[myieye]

I was playing with importing and updating various projects and found these changes to be valuable.

• Turning off the Pos.Name validation is something @hahn-kev suggested a while ago. It's blocking a few real projects I've played with locally.
• I see the catch in FromLexEntry(ILexEntry entry) trigger when entry.ComplexFormEntryRefs.SingleOrDefault() finds multiple items. We haven't decided what to do about that, but it's nice to at least see which entry is causing the problem. By doing so, I could modify the fwdata file to make the import happy. Deleting the entry refs in the UI didn't really help 🙃.
• The try catch in LexEntryHeadword(entry) is maybe excessive. It just felt good, beacuse I'm calling it from a catch block.
• I ran into other validation errors that didn't provide enough context for me to troubleshoot. Especially when we're complaining that something is null or empty, well....what is it?! 😆