[voicecall] Cast QObject::connect to bool.

This isn't harmful on Qt 4 (where it does return bool) but needed on Qt 5 where
QObject::connect no longer directly returns a bool to allow for the new-style
connect syntax.
[voicecall] Don't use QString::toAscii.

It doesn't exist in Qt 5.
[voicecall] Allow models to work with Qt 4 or Qt 5
[voicecall] Remove CONFIG += qdbus.

This works through dbus being in QT (which we already have) and CONFIG is
deprecated.
Merge pull request #10 from rburchell/master

Some fixups blocking Qt 5