Matrix refactor (breaking changes)

This PR brings several changes regarding matrices in NeoPZ Among them:

Distinction between symmetric/hermitian matrices for complex-valued matrices (discussed in #175 )
Decoupling of sparse matrix storage format and sparse solver
MKL now links with ILP64 interface and supports sparse matrix-vector multiplication
Users have now the responsibility to call SetSymmetry and SetDefPositive for their matrices
Small bug fixes

labmec / neopz