Remove formatting methods from QgsPoint

[nyalldawson]

QgsPoint has a bunch of methods for formatting a point to various strings, eg toDegreesMinutes. These should ideally be moved out of QgsPoint into a new QgsCoordinateFormatter class, with static methods for converting QgsPoint/V2/x & y doubles to the various formats.

Furthermore, the methods in QgsPoint are restrictive in that they always return both formatted latitude and longitude. Composer grids (and I suspect other code areas) need to then manually attempt to split the string back into separate lat/long components for rendering. It's inefficient and fragile, and there should be a way to retrieve just the formatted latitude or longitude.

[nyalldawson]

Fixed in master