Hide context tools when the model they match isn't "inspectable"

Also disable double-click & enter in this case.

Move ve.dm.Node#isInspectable to ve.dm.Model so annotations get it too.

Bug: 67176
Change-Id: Icecc0bf0ffc3e22f02fcbefac6aeb04e415c96fa
Merge "Hide context tools when the model they match isn't "inspectable""