improved context implementations to match assumptions made in Context

related to #268
removed bad overriden implementation of assignments which resulted in dcl x:int; x:= 2 to fail on an undefined value abort
Remove the `Chaos` basic action after a discussion with JCPWoodcock at
the June convergence workshop.
Kill an old (outdated) directory of the CML0 grammar in MediaWiki format
Merge commit '4fef4b885d7b6885b69bde88bea3d07b206b1d82' into jwc/base