Add support for isolation levels in DatabaseConnection
Add User.upsertPersonalInfo() method.

This performs an upsert to the persons table (update if the row to update
already exists, insert otherwise).
Avoid acessing personal info in login.jsp if it isn't loaded.
Make editPersonalInfo work for creating personal info.

fixes #11
Fix bugs in User.personalInfoExists()
Make User.upsertPersonalInfo return false on exceptions.
In LoginController.attemptUpdateInfo(), set errors
Git remove unused methods in User.java