Name kindle models in device classes

[coolharsh55]

The device.py classes categorise kindle models as BaseKindle (None), OldGenKindle, Paperwhite and Touch. It is not clear which of the kindle models this maps to. Consider this wikipedia article for a list of kindle models.

The kindle models can be named or described in the class documentation to make it clear which devices are utilising which classes for clarity. This can also help others looking for regexes to parse the clippings, who might not need the parser functions.