fix #983,expose latte availability to applets

--allow the applet developers to set at their
applet main file:

property bool disableLatteParabolicIcon: true

in order to disable any Latte functionality
concerning the parabolic icon

• allow the applet developers to set at their

main file:

property bool isInLatte: false

in order to be informed by Latte when they are
in a Latte containment. For what ever purposes
the developers need to adjust to their plasmoid.