comments #4 - model and migration

Signed-off-by: Alexander Skjolden <alex@plastboks.net>
comments #4 - list view

Signed-off-by: Alexander Skjolden <alex@plastboks.net>
comments #4 - create, edit - incomplete tests

Signed-off-by: Alexander Skjolden <alex@plastboks.net>
Merge branch 'categories' into develop