Fail sources with missing fields

[migurski]

From @trescube:

Here’s an example of a source that uses an unknown field name: https://github.com/openaddresses/openaddresses/blob/master/sources/us/mn/aitkin.json
In this case, it uses STREET for street which no longer exists and appears to use STR_NAME, STR_TYPE, and POST_DIR instead.

[trescube]

I just updated the source, here's it is before the update:

https://github.com/openaddresses/openaddresses/blob/e8114ce712a0d436e8e88d094feb71dc76bd5733/sources/us/mn/aitkin.json