First step to Python 3 support.

Some of the examples haven't been converted yet, also there is a metaclass
issue in MetaHasProps.
Fixed six.moves import.
Removed wrong error message.
Fixed sampledata download.
Fixed CSV reading in sampledata.
Fixed examples.
Fixed metaclass.
Fixed typo.
Added print_function imports.
Fixed bbmodel.py.
Fixed absolute import of wsmanager.
Fixed file writing in Python 2.
Fixed brewer.py in Python 3.

The iterator view ValuesView of OrderedDict is not JSON serialisable.