Enhance LogEntry creation in the forms at the site

[tlrh314]

When an instance is updated/changed via the Django Admin, the history page shows a LogEntry that specifies which fields were updated. The LogEntry that is kept in the views for forms submitted via the site (e.g. when myuser/Blogger or myuser/AffiliatedBlog changes) only shows that the instance was changed.

We can look into which fields in particular were updated, then add a comma-separated string of those fields to the LogEntry to keep a more verbose history in the admin interface.