Added ALARA format to nucname for write_alara use, corresponding tests

ALARA format is: "LL:identifier", where LL is the lower case atomic symbol. The identifier can be anything, based on what is found in the ALARA element library (which can be changed by the user). I have created what I believe to be the most useful starting point for an ALARA element library. It is subdivided into isotopes, using AAA as the identifier, yielding the form: "ll:AAA". This form is canonical to our R2S workflow, so it is definitely something that will be widely used (at least within CNERG and our user base).

When I wrote write_alara I thought I would be able to get away with using nucname.name for isotope printing because I did not realize the ":" is mandatory.

In any case, if this doesn't belong here I will just push it to the CNERG PyNE fork. If/when R2S makes its way to PyNE, this will become useful.