added CFGNode class
working towards new CFG framework:

* merge lambdas vastly simplified and integrated into cleanup
* Lambda::to() cannot crash anymore and return bottom : fn() if lambda
  is empty
* some refactoring
simlify + cleanup
checking for selfloop within merge_lambdas
clean up
Scope::sid -> Scoep::id
rpo_id -> sid
wip: CFG
temporary commented exit in CFG
added CFGView
ported domtree to new CFG infrastructure
ported looptree to new CFG infrastructure
clean up
working on type safety
more porting
more porting
it compiles - ship it!
wip
bug fixes
removing now superfluous features of scope