Change Forum navbar item to Questions

The projects navbar should mirror the one on the spring.io website.
Fix company name and website in footer
Fix "rm -rf" instruictions

Existing copy is wrong because "git rm -rf *" fails if there are any untracked files (e.g. target/). Changed to "git rm -rf `git ls-files`".
Gem installation instructions updated

Using "gem install" didn't work for me because of the Gemfile.lock that is in source control (presumably for a reason).
Fix directory name for sample pages
Add "gem install bundler" for people using vanilla Ruby