Include GVQ forward stylesheet to be available when importing metadata

[lushc]

GeoNetwork has a collection of XSL stylesheets that can be selected from a dropdown menu when importing a metadata record. The selected stylesheet will then be applied at the time of import.

A stylesheet to transform ISO19139 to GVQ has already been developed: https://github.com/lushc/geoviqua-inspire-tutorial/blob/master/19139-to-gvq.xsl

This forward stylesheet needs to be placed in the following directory: INSTALL_DIR/web/geonetwork/xsl/conversion/import

The following tasks need to be completed:

1. Place the stylesheet in the correct directory and test importing ISO19139 documents, selecting the stylesheet from the dropdown menu.
2. Test the validity of the transformed document.
3. Figure out the best method of distributing this stylesheet. Options are to create a new repo for it (and other GeoViQua stylesheets) & update README with instructions (ideal), or version it here and update the folder structure (not so ideal as it's already versioned elsewhere).