CMake and Conan stuff for Singularity 

RPath is adapted too.

[App/U] Unify command line version info output.

Now includes the copyright message and the version info with git hash.

Allow multiple meshes in project

Used in construction of mesh names in two places.
This unifies the name.

This is needed to repeat parts of the code solely for the
documentation purposes.

Rename bulk_node_ids and bulk_element_ids.
Use multiple meshes for setting the (heterogeneous) BCs.