LOT 1: Enabling the -Wsign-compare and -Wconversion warnings in MEDCoupling and MEDCo...

LOT 1: Enabling the -Wsign-compare and -Wconversion warnings in MEDCoupling and MEDCouplingRemapper packages.

Using size_t instead of int (where possible) in INTERP_KERNEL.

Eliminating warnings in MEDCouplingRemapper
- Eliminating Wconversion warnings
- Eliminating Wsign-compare warnings
- Using MeshType::MyConnType instead of int

Eliminating warnings in medcouplingcpp package
- Eliminating Wconversion warnings
- Eliminating Wsign-compare warnings