Login fields clear upon log out

- For easy logging in as a different user
Users can now change their own passwords - #181

- However, there seems to be something wrong with the method
  `AccountAccess.modifyAccount`. It's giving errors like:

  SQL Exception occured, the state : S0001
  Message: Incorrect syntax near 'Colin'.
Linted types.Account
Fixed small error in SQL query - fixes #181
Minor updates to DB access code

Added some preliminary functionality to grade access, and made the
DB access classes not exit when errors occur with the JDBC driver or
the connection to the SQL server.