Const-correctness & access rights

[aportelli]

That is going to be very painful, but I think that on the long run it can really pay in term of clarity for users and the way other softwares will base themselves on Grid. The idea would full scan all the declarations to insure:

• that function arguments & class methods are set to const when appropriate to reduce the risk of silent buggy variable changes
• that class members & inheritance have the right level of accuracy to avoid exposure of internals outside Grid