Issue#83

This pull request should address the refactoring for allowing the implementation to rank and select the mfa method to branch to by comparing the current requested ranked one (the current mfa transaction) with any previously fulfilled mfa authentications for the current CAS SSO session.

The only user-facing configuration change is the wiring of the existing mfa ranking configuration Map into the `OrderedMfaMethodRankingStrategy` bean like so:

```xml
<bean id="authenticationMethodRankingStrategy" class="net.unicon.cas.mfa.authentication.OrderedMfaMethodRankingStrategy"
          c:mfaRankingConfig-ref="supportedAuthenticationMethodsConfig"/>
```
This is interesting. breaking out of the loop early on does imply we either keep track of one thing only, or the set is sorted. While either may be true for the moment, I imagine there will come a time where CAS may need to keep track of multiple methods and perhaps even alias them for one another. To accommodate that silently. lets not break early on. Loop until you have exhausted everything in the set and that will have less side effects in the future.