Add ProjectionObj to ReferenceObj

[pspencer@…]

I would like to suggest that the Reference object be extended by the addition of
an optional Projection object.  The intention is to define the projection of the
reference map image so that applications can support viewing maps in different
projections while maintaining the same keymap.

The extent of the reference map would then be defined in the coordinate
system/units of the reference object's projection.  If no projection is defined,
then it is assumed to be in the projection of the map as a whole.

When the projection of the reference map is not the same as the projection of
the map, then the map's extents would be reprojected into the reference map's
projection before being drawn.

It would also be desirable to be able to draw non-rectangular bounding boxes on
the reference map when the projection has changed.  This could be done by
reprojecting points around the original bounding box and 'connecting the dots'.
 This could use a pre-defined number of samples or be controlled via a new
attribute of the reference map that would specify the number of samples to take
around the box.

This addition would slow down reference map generation, so it is important that
this functionality only be triggered if a projection is defined and the
projection is different from the map's projection.

[dmorissette]

*** This bug has been marked as a duplicate of 265 ***