Remove unneeded `meta` attribute on the model classes.

As per the comment which was removed, these don't make sense when the
cli isn't touching the model module; We still need them on master for
now, but we can get rid of them here.
Deleted a bunch of dead/bit-rotted/deprecated code.

Everything that remains actually imports cleanly.
Merge pull request #83 from zenhack/cleanup_meta_attr

Remove the `meta` attribute from the model classes.
Merge pull request #87 from zenhack/spring-cleaning

Spring cleaning
Fixed wrong number of format specifiers in haas.model.Headnode.__repr__.

Was 3, should have been 4, and was throwing an exception.
Merge pull request #88 from zenhack/Headnode.__repr__

Headnode.  repr