Add some SEO

[hamle365]

Some SEO should be added so that Dendrite can be properly indexed and found.

[hamle365]

• Meta titles
• Meta descriptions
• Keywords (no more than 10 per page)
• http://schema.org/
• 301 Redirects
• Custom 404 page
• Check only 1 H1 tag per page
• Give images descriptive ALT tags and filenames

[MattHeard]

Currently don't need 301 redirects.