Allow subclass modeladmin instances to define the way they render the changelist lines. Builds on the idea of a modeladmin supplying its own render_into_summary.

Fixes #1

Squashes 48d0bc1176323ac4d29b02929d2b68dc56fc251e and 909339b84ccabc72d83fbfa59442b797b9fe32a1
Original branch may still be at: https://github.com/kezabelle/django-editregions/tree/tickets/1