Feature/ipboard login refactor

This module refactors the ipboard_login module by @ChrisTruncer to use a new LoginScanner class designed to abstract the heavy lifting in a reusable and testable manner.

@ChrisTruncer if you could review and test this to please make sure I didn't break anything that would be great! Thanks

branched off of https://github.com/rapid7/metasploit-framework/pull/3697
I believe the "/" between #{uri} and index.php... should be removed.  If left with the default uri value of "/forum/", it makes a request that will fail the login check since there will be a double slash ("//") in the uri.  I don't believe "normalize_uri" is exposed for use here, is it?