Abstract pages and prototype pages should be auto-exported to a separate file per page

All pages added to the hst:abstractpages and hst:prototypepages nodes are exported into one big file (abstractpages.xml and prototypepages.xml, respectively). This is very cumbersome for developers, as merging differences in this file gets hard in big projects.

Instead, these pages should be exported to a separate file per page in subfolder 'abstractpages' and 'prototypepages'. This already happens for pages in hst:pages.