Merge pull request #9 from rburchell/master

Simplify voicecall packaging
[voicecall] Port to QOfono.
[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] Disable Q_EXPORT_PLUGIN2 for Qt 5.