Added the functionality of creating a key pair based off of account numb...

...er or account address as well as from seed bytes.

After thinking about it more and a few of sublimator's comments,I came to the realization that the java version shouldn't mirror the exact behavior of the JS function (because of the different nature of the languages).  

Because of the strong typing nature of Java I thought it would be best to let the client of the Seed class determine which method / case they would like to use and eliminate any ambiguity in letting the function determine what the client is sending in.  

TODO: Find out exactly what the check should be in the createKeyPairFromAddress should