In the TOSCA functions modal a user can select a property defined on the component itself. This story is to enable the user select a component instance that has been added to the component and select a proprety of that component instance

• Add a drop down box with title "Property Source" which shall only be visible when a get_property is selected from the "TOSCA functions" drop down list
• Populate the drop down list with "SELF" and the names of the component instances in the component
• Populate the "Property" drop down list with the list of properties defined on the selected property source that are of the same type as the property being set
• Add all necessary handling to persist the value as selected and render it correctly in the generated tosca