Merge pull request #1 from special/master

[nemo-qml-plugin-messages] Port to Qt5
[nemo-qml-plugin-messages] Fix incorrect name in packaging
[nemo-qml-plugin-messages] Remove deprecated MessagesContextProvider element

This is replaced by a dbus interface provided by commhistory-daemon,
which can be used directly from QML. All affected software has been
changed to stop using this element.