add annotations on the map for measurement tools

[bfischer-hei]

transferred from http://trac.osgeo.org/geomoose/ticket/149

Currently when using the measurement tools the distance for each segment is displayed in the service area. In addition to the segment distance displayed on the left side of the screen, it would be useful if a text label was displayed on the map as a user draws each segment.

eg o--100--o---150---o