Multimedia model and related functions in multimed.c

After quite some time I've managed to pull through the different functions in multimed.c and created the tests in check_multimed.c
Note few significant API changes that need to be propagated carefully into the code: 
calls to multimed_nlay (previously nlay_v2) and multimed_r_nlay (_v2 is removed), init_mmLUT have changed, we pass now the *cal, *cpar, *vpar, etc. 
For ... loops for the cameras are now inside those functions. 
Note that the mm_np structure remained untouched, the changes are by far more complex than previously thought. At the moment the default mm->nlay = 1 which means that we work with air - glass (1 layer) - water. It is possible to extend it immedinately to mm->nlay > 1 and have multi-layer-glass