refactor validateSettings()

[jwildfire]

Update the field check to use the field_mapping column in settingsMetadata

[jwildfire]

Do this after #113 is done. Also include a tweak in validateSettings to get rid of the hack-y pattern detection approach we were using.

[jwildfire]

Also used the new hasField() and hasColumn() functions to streamline things. Need to add support for vectorized settings (#170), but can tackle that later.