Now possible to get correct ensureRequirements when inheriting Print<backend>ASTVisitor class.

Added two small functions: classNameString() and namespaceNameString() which is used by postVisit(SequenceNode&) function.
PrintCUDABackendASTVisitor class now inherits PrintCPUBackendVisitor.

Also removed the anonymous namespace in the CUDA backend printer.
Added the functions for name of runtime class and namespace.

According to the two previous commits.