TASK: Convert Text columns in Account model to String. Fixed #11.

Some database will reject length so we should convert
to String, and since Text is more useful for textarea kind of data,
it makes sense to use String.

We may convert to unicode at some point.
TASK: Restrict first/last name to 30 chars. Fixed #10.

Because of this bug https://groups.google.com/forum/#!msg/sqlalchemy/eyESpu7mZc0/C3OfTBdPkzYJ, I cannot use Column(String(30)) to determine which field caused the exception.