Only create pgcrypto if it doesn't exist

Necessary because we may have to create the extension manually outside
of migrations if we are not a database administrator.
Add notes for deployment
Fix opening multiple tabs from one 'v' press

Problem was events were not being unbound, so if the home page was
viewed, then another page, then the home page again, there would be
two listeners. Introduce base view class that handles removing
children.