Load balancing is performed on a list of discrete functions that live
on a common mesh. Their values are transferred according to the new
partitioning of the mesh.

It allows to get the mesh that carries a discrete function

Cells and nodes look ok.
Faces (and probably edges are not correctly exchanged yet)

 [ci-skip]

And continue fixing ConnectivityDispatcher issues when called in
parallel

- now this information is computed when needed (load balance)
- closes #11

This is useful to check mesh partition/load balance

- Add simple CMake recipe
- Add PartitionerOptions
- Separate ParMETIS partitioner from Partitioner

Feature/eigen3

See merge request !201

This kind of boundary condition type is useful for PN solvers for instance.

- the environment variable PUGS_INSTALL_DIR is no more used
- also fix HDF5 detection on ubuntu for plugins

Change strategy for modules registration to the ModuleRepository

See merge request !200