Fix container notch and move control disappearing after a move

[janscarton]

Fixes concretecms/concretecms#12353.

When you move a container, its title notch and move control vanish until you reload the page. That's the first bug below. While I was in here I also fixed a related one where the move handle stays put but stops responding to clicks.

1. The notch disappears when you move a block. Block.move() called my.getContainer().remove() and then, for a non-wrapping block, re-inserted only the inner element — so the container wrapper that carries the notch (and its move control) got thrown away. Now the wrapper is captured up front and detach()ed instead, so it survives the move and goes back in as a unit.

2. The drag handle stops responding. The ConcreteMenu click-proxy overlay (z-index 500) could end up painted over the notch's move handle, swallowing the mousedown so pep never starts a drag. Two parts: bindNotchMenu() clears stale .concreteMenu handlers that pile up across drag cycles (ContainerBlock and Layout don't keep a reference to their menu, so it isn't torn down on scanBlocks reset), and the move handle gets position: relative; z-index: 501 so it paints above the proxy.

Both show up on plain within-area sorting — bug 1 is the exact repro in the issue.