facts: provide Fact as an inline on FactCategory

closes bss/dr.botzo#14

facts/admin.py

@@ -4,5 +4,17 @@ from django.contrib import admin
 from facts.models import Fact, FactCategory
 
 
+class FactInline(admin.TabularInline):
+    """Inline admin form for facts, for inclusion in fact categories."""
+
+    model = Fact
+
+
+class FactCategoryAdmin(admin.ModelAdmin):
+    """Admin pages for the FactCategory model."""
+
+    inlines = [FactInline]
+
+
 admin.site.register(Fact)
-admin.site.register(FactCategory)
+admin.site.register(FactCategory, FactCategoryAdmin)