Add contents to qt.conf file for macOS
The default Qt plugins directory is expected to be 'paraview.app/Contents/plugins', but we are packaging Qt plugins into 'paraview.app/Contents/Plugins'. On case-sensitive file systems on macOS, the change in case of 'Plugins' causes the platforms/libqcocoa.dylib plugin to not be found and leads to a crash. Fix this by specifying our non-default Plugins directory in qt.conf.
Fixes #52 (closed)