Implement new plugin mechanism

Implement new plugin mechanism

moc can now embed meta information about the plugin
inside the plugin itself. This information can
be queried by Qt without having to load the plugin.

Source compatibility with the old plugin loading
mechanism is still there, but will be removed before
Qt 5.0.

Change-Id: I03e4196ddfed07d0fe94acca40d5de8a6ce7f920
Reviewed-by: João Abecasis <joao.abecasis@nokia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>