container_block: do not show its boxes at add_block view
container_block: fix edition layout
container_block: do not cache

Container block was not updated when its child changes.
Setting cacheable? to false in container_block to avoid this problem.
container_block: avoid cyclical reference

(ActionItem2943)
container_block: toggle move of children on hover
Merge branch 'AI2943_container_block_fixes' into stable

Conflicts:
	plugins/container_block/lib/container_block_plugin/container_block.rb
	plugins/container_block/public/style.css
	plugins/container_block/test/unit/container_block_plugin/container_block_test.rb
	plugins/container_block/views/blocks/container.rhtml