Add new SEO package

Add meta descriptions, open graph, sitemap.xml, more perspicuous titles,
etc. Addresses most concerns in #355.
Merge branch 'telescope-master-seo'

Conflicts:
	.meteor/packages
	.meteor/versions
	packages/telescope-seo/package.js
	packages/telescope-seo/seo.js
	packages/telescope-seo/versions.json