add PSR name property to Spectrum

[paulthebaker]

It would be helpful to have more useful metadata bundled in the hasasia.Spectrum object. This would make it easier to save and reuse spectra by pickling a list of hasasia.Spectrum objects.

In particular for plotting and sorting, the tutorials zip lists of hasasia.Pulsar objects and hasasia.Spectrum objects together for loops in order to get the Pulsar.name. A name property could be added to the spectrum at creation. Other metadata may be helpful too.