Updating User index page & demo server for FS

This PR addresses ticket https://trac.openmicroscopy.org.uk/ome/ticket/10956 - adding an introduction to OMERO 5 and link to the OME 5 product page*, and making it clear that the Demo server is not available for FS as yet, but will be in the future. Also minor change to main index page.

Pages will be built under /support/omero5-staging/ for testing.


*This won't work until I update the omero_plone extlinks in the config and make the new plone pages public, it just points at the current OMERO product front page at the moment.