Extended number of states for BEAST 2 outputs

In principle, any number of states should theoretically be permissible in BEAST 2.7 XML inputs, since the states are specified as sequences of probabilities rather than with one-character symbols. But even with sequences encoded in this way, BEAST 2 still requires code maps (for some reason), so we are limited by the space of allowable single-character symbols. Previously, teiphy restricted the set of BEAST state symbols to 0-9 and a-z. This release adds A-Z to the symbol set.