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 miss specs for the ```IPBoard ``` specific behavior on #attempt_login? Is it okey "as-is"?