Feature/algebra coverage

These tests concern
- libraries checking
- method and preconditioners checking
- plugging to the libraries
- deal with the availability of PETSc

Also add numerical tests using PETSc and builtin solvers

It is just an artifact to fix small (irrelevant) coverage issues

The `columnIdToValueMap()` function was designed to access to the
sparse description of lines of a `SparseMatrixDescriptor`. This was
added when interfacing with `PETSc` but finally the coupling is made
though `CRSMatrix`.

Change a bit the interface to ensure that matrix structure cannot be
modified once the matrix is built.

Actually the interface of the underlying `Kokkos::StaticCrsGraph` is
quite crappy, especially to prevent matrix changes.

Replacing `Kokkos::StaticCrsGraph` class by an appropriate builtin one
should be considered: one could then provide a better interface, and
offer a better coupling with external linear algebra.  Also, this
would reduce the direct dependency on Kokkos.