Adds a custom property to a report element.
POST /documents/<documentID>/reports/<reportID>/elements/<elementID>/properties
Request body: the property to add.
Response type: application/xml or application/json
The response is a message stating the success or failure of the request.
POST /documents/1234/reports/1/elements/100/properties
Request body:
<property key='NEW_KEY'>MyKeyValue</property>
Response:
<success> <message>The resource of type "Property" has been successfully created.</message> <id>NEW_KEY</id> </success>