Programmatically add terrain

[plusk01]

In addition to pulling the aerial imagery for a given lat/lon, add terrain data.

Consider using terrain.party (http://terrain.party/api/export?name=rock&box=-111.633553,40.268464,-111.637865,40.266012) to get heightmap images.

Also, this gazebosim answer suggests making a .dae using meshtool.

The problem with bringing in a DEM into a gazebo is that gazebo only supports 8-bit DEMs, so low-resolution.