fallback to rhino if no default javascript is found (#280)

[artlog]

• avoid NullPointerException
• always default to a non null defaut scripting implementation
  • default to ErrorMissingScriptEvalauator to fail a first unsupported scripting usage
• try to uee rhino if no js is

[artlog]

to fix : incorrect defaut if no graaljs and no rhino ( defautImplementation can be reset to null ).