Change the representation of matrices

The code is only partially changed; it will not compile
Deny copying Matrix objects (Known bug: no deep copy ==> double free())
Add function: copy to contiguous memory area
Fix saving matrices into files
Fix generating random matrices (do not reinitialize the seed)
Fix test-matr equality
New test cases: matrix: RndEq, Identity
New test case: matrix inversion
Tidying
Fix multiplication bug: destination not initialized to 0s
Change matrix representation

The new representation allows discontiguous storage of matrices.
Merge branch 'devel' into seprows