Add custom year validation messages

[malberts]

From #79 (comment) and #55

[malberts]

I started looking at this, but there seems to be different behavior between Firefox and Brave.

Branch: https://github.com/ProfessionalWiki/WikibaseExport/compare/year-error?expand=1

It's possible to change the validation message and it's also possible to trigger the validation message as the user types. The current state of the branch has an issue where the validation message doesn't auto-close in Firefox and it also looks like it's not updating to the correct error when you go from an invalid value to another invalid one, or if you go from an invalid one to a valid one. The moment you click away and back, or leave the invalid value and submit, then the correct one shows up.

I'll come back to this once other more important tasks are done.