Support namespaces for qtcpp generator

[jryannel]

There shall be common helper functions for the qtcpp generator to create an open and closing namespace.

Additional a helper function needs to be available to convert a type into a namespace type.

[jryannel]

A module with org.example.echo should result into a namespace of

Opening a namespace {{module|open_ns}}

// open namespace org.example.echo
namespace org { namespace example { namespace echo {

And the closing namespace {{module|close_ns}}

// close namespace org.example.echo
} } }

And the the use case of using a nested namespace {{import|use_ns}}

using namespace org::example::echo

[jryannel]

See 1496c73
and 8db91c5