Changed slugs to match the values used in the reference data.

Changed the slugs used by the test factories for each model so they match
the values from the reference data that is used to populate a new database.
Added audit fields to each model.

Added fields for the typical audit pattern: create_by, created_on,
modified_by, modified_on to each model class.

There were two motivations for this change. The first was obviously
adding the ability to track changes to the database, primarily by
staff responsible for content changes, particularly to tables such
as Species which should remain standardised and change relatively
infrequently. Secondly modified_on will be useful for tracking new
Checklists and edits to Entry objects. This will be useful for any
news site that want to make the published data quasi-static, where
news is typicaly only published a couple of times a day. In this
case the data would be published as HTML pages or converted to
some intermediate form that reduces the processing overhead when
a page is rendered - which is particularly heavy for information
such as which Species were added to the current yearlist.
Updated version number for release
Merge branch 'release-0.4.0'