Add error support to action proposal, plus convenience functions
Add error support to action proposal, plus convenience functions

Prototype with extra conveniences for invocation, isTargetSupported
and metadata.

Also added "parameters" parameter to metadata, since it applies to a
particular invocation input.

enthought/qt-mobility,qtproject/qt-mobility,tmcguire/qt-mobility,qtproject/qt-mobility,tmcguire/qt-mobility,tmcguire/qt-mobility,kaltsi/qt-mobility,tmcguire/qt-mobility,kaltsi/qt-mobility,enthought/qt-mobility,qtproject/qt-mobility,kaltsi/qt-mobility,enthought/qt-mobility,KDE/android-qt-mobility,kaltsi/qt-mobility,qtproject/qt-mobility,KDE/android-qt-mobility,enthought/qt-mobility,qtproject/qt-mobility,kaltsi/qt-mobility,enthought/qt-mobility,tmcguire/qt-mobility,kaltsi/qt-mobility,enthought/qt-mobility,KDE/android-qt-mobility,KDE/android-qt-mobility,qtproject/qt-mobility