qt4-webos: disable both webOS QPA plugins

Signed-off-by: Simon Busch <morphis@gravedo.de>
qt-palm-plugin: add recipe for the the external QPA plugin

Signed-off-by: Simon Busch <morphis@gravedo.de>
luna-sysmgr: add dependency on qt-palm-plugin

Signed-off-by: Simon Busch <morphis@gravedo.de>