Session management: Use CSS locator based on form inputs rather than attributes
Created by: Zapotek
When trying to identify the login form for submission, use a CSS locator that is based on the user-specified form inputs, rather than relying on the default locator that uses form attributes, as they can be dynamic and thus unreliable.
See: https://github.com/Arachni/arachni/issues/824#issuecomment-279993070