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"/>
```
Not restarting the flow, but continuing the flow without launching the requested mfa subflow, since the requested mfa method happens to be `WEAKER` than any other previously fulfilled once, hence satisfying the mfa requirement already... Unless I totally MISS some very important piece of info about how this should work.