Display items and tags using django-tables2

Use django-tables2 to display information about items and tags. This was already
being done by hand, but django-tables allows the process to become more
automated. Less hand-written HTML, more auto-generated HTML.

There are now three datasets being rendered with django-tables2: items, tags,
and lends. All three datasets are lacking a column that provides links to view,
edit and delete the relevant object. It may prove useful to create synthetic
columns within the models themselves.