Option to output an orthophoto from filtered point cloud

[andrewharvey]

It would be nice to configure ODM to output an additional orthophoto created from a filtered point cloud of the users choosing. For example if I want an orthophoto based on the ground+building (excluding vegetation) classified point cloud.

This would allow an orthphoto which reveals detail underneath the tree canopy, where the source images were able to capture details under the canopy, which for sparse trees and especially with oblique capture angles can work out quite well.

Also discussed at https://community.opendronemap.org/t/creating-orthophoto-from-ground-classified-point-cloud/20865