Add maidenhead precision logic to Position

[CBielstein]

Description

Position class currently does not have an automatic encoding of gridsquare to be the correct specificity. This can be a problem if a 4-char gridsquare is decoded and then attempted to encode later. This would add additional precision (which may not be very accurate) to the location.

Another example is decoding from a lat/long coordinate with ambiguity.

Consider using the ambiguity value in encodes and decodes.

Acceptance Criteria

• Maidenhead gridsquare decode and encode results in the same precision of gridsquare
• Maidenhead encode does not result in a more precise location than geocoord with ambiguity