Fix not showing Contexts without declarations in outline view

For example in the following code the members of N::C would not show up:

namespace N {

class C;

}

class N::C {

char c;

}

int main(int, char**) {}

There is still the problem that N::C gets listed after main(), but there
are also other ordering problems. This will require sorting based on the
declaration location of the OulineNode

REVIEW: 123586