Parse (and optionally generate) shorter positions with ambiguity

[ge0rg]

As reported in https://github.com/ge0rg/aprsdroid/issues/76, the spec allows the removal of whitespace in the longitude according to the ambiguity defined in the latitude, e.g.:

4903.__N/07201.75W-

This should be supported by the parser in PositionParser.parseUncompressed, and optionally be generated by the string formatter of Position.getDMS.