[+AS] Use clean env when shelling to heroku tool belt.

Otherwise, this results in Bundler::RubyVersionMismatch since heroku-toolbelt needs 1.9.3 to run.
Remove the default footer.
Widen GitHub repo URL to accept all characters
that are accepted by GitHub.
[+SP] Let users edit their GitHub repo URL links.
[+SP] Beta corner ribbon.

Feel the Web 2.0.
[+SP] Add real content to the home page