Separate Kaminari theme

Prevents ActiveAdmin's pagination from being overriden by any
customizations made to the Kaminari views in a Rails app that uses
ActiveAdmin. Fixes gregbell/active_admin#1126.
#2701: fix documentation inaccuracy
update 7-sidebars.md
update 10-custom-pages.md
update 11-decorators.md
update 12-arbre-components.md
add the IRC channel to the README
Merge branch 'master' into kaminari-theme

Conflicts:
	lib/active_admin/views/components/paginated_collection.rb
Rename Kaminari theme to active_admin
sortable has-many
Merge pull request #2656 from igorbernstein/has_many-sortable

sortable has_many
Merge pull request #2048 from jbhannah/kaminari-theme

Separate Kaminari theme
tabs -> spaces
fix z-index priority for parent menu items

fixes #2702