JsInline: added method traverse() to all nodes
JsInline: added class JsGwtVisitor
JsInline: added class JsGwtModVisitor
JsInline: use SmartList instead of SingletonList when `new JsBlock(statement)` called

Reason: it is ok to insert in a block after AST was created during translation.
For example, inliner can insert inlined body in such block.
Thus immutable SingletonList isn't appropriate.
JsInline: removed old inline logic
JsInline: added class CloningVisitor
JsInline: added class RenamingVisitor
JsInline: added class NameCollector
JsInline: added class ReturnCounter
JsInline: added class ReplaceReturnVisitor
JsInline: added class FunctionInlineMutator
JsInline: added JsName static ref for function
JsInline: added class InlineableResult
JsInline: made break labels optional
JsInline: added JsInliner (inlining entry point)
JsInline: added class FunctionCollector (collects inline functions)
JsInline: JsInliner recursively processes AST
JsInline: save block contexts to stack

Reason: need to be able to insert inlined body
before current statement (that might be
distant parent of node currently being
processed)
added getCurrentNode() method to context
JsInliner