Remove all warnings with gcc 8: memset et memcopy une now reinterpret_cay<char*> and we remove restrict fir target and source in p2P

This allows altering the LICENCE text without changing all files. It should
avoid merge conflicts in the future.

 - Divide the FRotationCell inner data layout into two sub-types:
   multipole_t and local_expansion_t. Two class attribute are accessible
   through the `getMultipoledata` and `getLocalExpansionData` methods.

 - Change FMM operators signature to take advantage of the new
   layout. The operators only take as parameters the data they may need
   instead of the whole cell. For instance (simplified):

   void M2M(CellClass* parent, CellClass** children);

   becomes

   void M2M(multipole_t*  parent_m,    symbolic_data_t* parent_s,
            multipole_t** children_ms, symbolic_data_t* children_ss);

add an additional P2P: P2POuter which compute the P2P between neighbors (possibly in mutual way) but not the inner P2P in the target leaf

Remove some warnings, and split P2PR which is P2P only for one over R and P2P which can accept a matrix kernel (which can be one over R or anything else), both approaches support SSE and AVX but have not been tested.

Rotation Kernel Oups in the name of rotation functions and add a particle to particle no mutual interaction in the kernel.

Finished the rotation kernel, BUT need to make an optimized one and remove computational tests. The current version is a copy of the papers formula