COVE Validation check: Check that dates of death of natural persons are sane

[siwhitehouse]

Check that dates of death of natural persons are sane. As a start I'll suggest:

• no one has a date of death in the future
• no one has a date of death more than 120 years after their date of birth

which are largely in keeping with the checks that we have implemented for date of birth.

@odscjames we added a similar set of checks for date of birth. It looks as though we made changes to the code here for the general case and then added configuration to the cove-bods repo. Is it ok for me to raise the whole of the issue here, or should I split it into the two issues?

[stevenday]

Closing as a dupe of #59 which seems more complete