Properly implemented JS GlobeCoordinateValue::toJSON and newFromJSON

Allows round tripping with the backend implementation now. Precision is not yet implemented.
Moved the problem of dealing with precision from globeCoordinate.js into GlobeCoordinateValue
since "globeCoordinate.js" should not really know or care about the problems of the "backend"
or anything else Wikibase related.

Change-Id: I6b0e3584996a0709de81b37ac07659d6b5bd2c97
Merge "Properly implemented JS GlobeCoordinateValue::toJSON and newFromJSON"