add class edition support

[jimy-byerley]

function edition is supported in uimadcad through

• 1 detecting the AST node as the function object definition
• 2 allowing to enter the function calls, by freezing the calling context and spawning a new incremental interpreter in the function scope

class methodes should be editable too through the same kind of scope edition, a special care should be taken to the objects attributes: should it be always in the display list ? how their name should be taken into account to allow them to be selected and used easily ?