Client plugin should be installed into defailt import dir

[Michał Sawicz]

The client plugin is currently installed in the shell's plugin dir, it should be installed in the default Qt import dir instead - i.e. `qmake -query QT_INSTALL_QML`. Unfortunately due to bug https://bugreports.qt-project.org/browse/QTBUG-29987 it's not available directly in CMake.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: qtdeclarative5-unity-notifications-plugin 0.1.1+14.04.20131030.1-0ubuntu1
ProcVersionSignature: Ubuntu 3.11.0-12.19-generic 3.11.3
Uname: Linux 3.11.0-12-generic x86_64
NonfreeKernelModules: nvidia wl
ApportVersion: 2.13.2-0ubuntu2
Architecture: amd64
CurrentDesktop: Unity
Date: Tue Jan 28 10:47:46 2014
SourcePackage: unity-notifications
UpgradeStatus: No upgrade log present (probably fresh install)