converted links to use root_url config parameter, removed dead links (downloads)
fixed dead-link in simulations/index.html
fixed background images in simulations/
Merge remote-tracking branch 'upstream/gh-pages' into gh-pages

Conflicts:
	_config.yml
	_layouts/default.html
	simulations/index.html
Merge remote-tracking branch 'upstream/gh-pages' into gh-pages
Added Glasgow simulation screenshot.
Merge remote-tracking branch 'nfvs/gh-pages' into gh-pages