Make Modifier.component_type radio buttons in admin

Reverts the earlier removal of these radio buttons (and thus
replacement with the default dropdown) because of a bug in
grappelli's generic foreign key lookup when using radio buttons;
I now have a patched grappelli so I can put the radio buttons back.
Move modifier table generation into a template tag
Calculate max modifier magnitude and pass it along
Replace modifier classes with percentage based ones
Share capture of hero_component between patterns
Add defence list and detail views
Link to defence list from index