JS backend: move StringBuilder to java.lang. Fix append return type.
JS backend: refactor ClassTranslator
JS backend: add debug info into several tests
JS backend: first step of remove _c object from output code.
createClass -> createClassNow, createTrait -> createTraitNow, createObject -> createObjectNow
First argument of new createClass() is function, which return array of parent classes.
JS backend: complete remove _c object from output code.
JS backend: add simple enum test
JS backend: rewrite FileDeclarationVisitor use kotlin
JS backend: drop ClassAliasingMap from ClassTranslator
JS backend: inline ClassDeclarationTranslator