Merge pull request #15 from YfLn/master

just merging
Updated user.server.model.js to require a unique username
Merge pull request #19 from YfLn/master

Pulling from Master
Merge branch 'Richard' of github.com:YfLn/CEN3031FA14 into Richard
Merge pull request #18 from YfLn/Richard

The 'username' field required a 'unique' attribute in order for the final test to pass.