The War on RippleAddress - The battle of Seed

** DO NOT MERGE THIS AT THIS TIME **

`RippleAddress` and its multiple personalities have been a thorn at our side. This is the first steps towards splitting it into single-responsibility classes.

The seed generation has been removed from `RippleAddress` and moved to a function called `RippleAddressSeed`. The name is *temporary*: we can come up with something more appropriate and decide where this fits in the project hierarchy.

With that said, the code compiles and passes all unit tests. I am hoping for a thorough review, in case I missed (or borked) something. Comments or suggestions for improving this are, of course, welcome.