Added `-[AIService supportsPassword]` which determines if the service should display password fields at all and changed `-[AIService requiresPassword]` to determine whether it should ''insist'' upon a password before continuing the connect process. This allows Jabber and IRC accounts to be password-optional. Fixes the spurious password prompts for Jabber accounts which will be using GSSAPI, fixing the issue described as a side comment in #8680. Refs #8680.
git-svn-id: svn://svn.adiumx.com/adium/trunk@22030 1c916fce-81e2-0310-a464-8ca513f45935