Network Filesharing: Refactor foreach and emit, smaller improvements

Summary:
Compile without emit and foreach.
The private variables inside the model are prefixed with _, because
the userList variable shadowed class definition. This should clear things up.

And some better overloads and const qualifiers.

Test Plan: Compiles

Reviewers: #dolphin, ngraham

Reviewed By: #dolphin, ngraham

Differential Revision: https://phabricator.kde.org/D29118