twi: add support for USCB_1 module on devices that support it

This is an initial pull request, I think a full review and some discussions needs to take place before this can be merged, but I want to get the "process" started.

There are some major restructuring, plus I have made some changes to how the "UCBxCTL1" and "UCBxCTL0" are initialized, therefore you will see some commented out lines related to those, to make you extra aware of those changes.

The include part in Wire.cpp I also need some help on, a bit unsure how it shold be, as you can see, I have just commented it out now, but it works in my example.

You can also see that I've removed some hardware serial from usci_isr_handler.*, it does not seem to be needed, but I have not tested this, I've just seen that it compiles. If you want to do that change, maybe it should be a separate pull request ?