[API BREAK] Use qt_plugin for QMF plugins instead of reinventing our own architecture.

We now use a subdirectory of Qt's own plugin location instead of reinventing our
own idea for that. This also involves the removal of the (now useless)
QMail::pluginsPath.

Change-Id: Ib54ad6186031c689eccb5631a8cf25a4afa0d354
Reviewed-by: Valerio Valerio <valerio.valerio@jollamobile.com>
Reviewed-by: Robin Burchell <robin+qt@viroteck.net>
Make URL opening function in a cross-platform world.

Change-Id: I7f4bee6fccf1e2a805cc7e9899ae16a6e15caa8d
Reviewed-by: Valerio Valerio <valerio.valerio@jollamobile.com>
Reviewed-by: Robin Burchell <robin+qt@viroteck.net>
Fix compilation of benchmark on Linux.

We need qmfclient-private for QCop headers.

Change-Id: Iff17d3bb974eea16196e05fc66386ad71d7bc3d4
Reviewed-by: Robin Burchell <robin+qt@viroteck.net>