Editor / Add a function to create a add subtemplate button outside an element control

[fxp]

Currently add subtemplate button is only available in the last element of a type. Add a generic function to create a custom button to be place outside element scope (eg. at the head of a section).

[fxp]

Commit ac4c1ce077de91de51b12807fc12e96130ce7225

Example: Add a button to add point of contact in identification info

            <xsl:copy-of select="geonet:makeSubTemplateButton(gmd:identificationInfo/gmd:MD_DataIdentification/geonet:element/@ref, 
                                                                    'gmd:pointOfContact', 
                                                                    'gmd:CI_ResponsibleParty', 
                                                                    /root/gui/strings/addXMLFragment,
                                                                    /root/gui/strings/addXMLFragment)"/>