Multiple `is_prime` implementations

[VincentRouvreau]

I can see multiple _is_prime implementations in Persistence_matrix module:

• https://github.com/GUDHI/gudhi-devel/blob/f23c15477d65209ba682b36d898b3770234598a9/src/Persistence_matrix/include/gudhi/Fields/Zp_field.h#L405

• https://github.com/GUDHI/gudhi-devel/blob/f23c15477d65209ba682b36d898b3770234598a9/src/Persistence_matrix/include/gudhi/Fields/Multi_field_small_operators.h#L493

• https://github.com/GUDHI/gudhi-devel/blob/f23c15477d65209ba682b36d898b3770234598a9/src/Persistence_matrix/include/gudhi/Fields/Multi_field_small.h#L390

• https://github.com/GUDHI/gudhi-devel/blob/f23c15477d65209ba682b36d898b3770234598a9/src/Persistence_matrix/include/gudhi/Fields/Multi_field_operators.h#L440

• a new implementation that comes with Ripser new module : https://github.com/mglisse/gudhi-devel/blob/8cab8c9e3695846278f3b8fd8095715bbc8e5950/src/Ripser/include/gudhi/ripser.h#L158

We could also take the opportunity to homogenize the behaviour of Ripser/Matrix/Persistent_cohomology when passing a homology coefficient field.