cleanup
template: specify content type for scripts and stylesheets

While these usually are JavaScript and CSS, it is good practice to
make that explicit.
template: do not use http-equiv="X-UA-Compatible" with "chrome=1"

This is meant to force the Chrome Frame plugin, and is deprecatd.
template: include MathJax by default
update.g: output homepage URLs for package dependencies
template: add hyperlinks to deps, and also list suggested deps
Merge branch 'gh-pages' of https://github.com/fingolfin/GitHubPagesForGAP into gh-pages

Conflicts:
	_data/package.yml