Allows elevation properties to be set for vector layers, including:
- altitude binding
- altitude clamping
- extrusion
- scale
- offset
These properties can be set through the new "Elevation" tab in
the vector layer properties dialog
users to set a manual offset to apply to point cloud z values
This allows for adjustment of the elevation of point clouds, eg so that:
1. They match nicely with point clouds from other datasources
2. Users can use point clouds from sources with arbitrary z values,
eg. a point cloud made by opendronemap without any actual reference
z values available
