added 'using namespace' inside generic lambdas to workaround an intel compiler bug

This is related to #31 (closed) .

Due to an intel compiler bug (it's probably a bug since all other compilers I've tested do not have this issue and it should not be related to compiler flags) a small workaround is necessary in nested functions calls involving generic lambda, see also my stackoverflow question. Especially this occurs in nested Hybrid::forEach calls due to the usage of the subnamespace Hybrid that is not found inside of the lambdas.