Add SVG logo and make it scale

Resolves #54
Add logo to navbar

Resolves #64
Redirect to /forks if logged in

Resolves #65
Remove navbar on homepage

Resolves part of #64, but could be DRYer with a nested layout. However, brainfail.
Merge branch 'refs/heads/master' into logo-tweaks

Conflicts:
	app/assets/stylesheets/application.css.scss
Merge pull request #70 from theodi/logo-tweaks

Logo tweaks