This class can be used to retrieve a list of available assets.

Currently returns only the highest version available for assets
that are not experiments.

This model can be used, for example, to populate the content of
combo boxes when there's a need to show a list of available
dataformats.

- Moved test into a class
- Use fixture for model creation

Can be used as a starting point for the field editor.

beat.editor will be using pytest

Closes #151

This will currently fail as errors are raised. This patch fixes
this by setting the raise_on_errors flag to false.