Login system

[wbprice]

Users and candidates should be able to login using a passphrase in a XKCD-936 compliant way. Admins use email address and password.

[ttavenner]

Surveys can be accessed via a random passphrase i.e. /results/ElevatorTurnip. This allows the user to share results and revisit them. At the end of the survey the user will also have a randomly generated private string that allows them to edit their results. Something like /results/edit/a8d24e7. Candidates will be emailed this private URL when the survey is opened to them. The user will have the option to have this URL emailed to them when viewing their results.