annotation connectors: editable/non editable

[tuurma]

Allow to specify on pb-authority custom connector if a "new entry" button and editing form should be available for this register entries. In the example below the property is called edit and will only be respected if connector="Custom"

 <pb-authority-lookup subscribe="transcription" emit="transcription">
                                        <pb-authority connector="Custom" name="organization">
                                            <pb-authority connector="GND" prefix="gnd"></pb-authority>
                                        </pb-authority>
                                        <pb-authority connector="Custom" name="place" edit="edit">
                                            <pb-authority connector="GeoNames" user="existdb" prefix="geo"></pb-authority>
                                        </pb-authority>
                                        <pb-authority connector="Custom" name="term">
                                            <pb-authority connector="GND" prefix="gnd"></pb-authority>
                                        </pb-authority>
                                        <pb-authority connector="Custom" name="person"  edit="edit">
                                            <pb-authority connector="GND" prefix="gnd"></pb-authority>
                                        </pb-authority>
                                    </pb-authority-lookup>