Fix MAGN-4710 Errors/Warnings are not getting cleared from nodes

This pull request fixes defect [MAGN-4710 Errors/Warnings are not getting cleared from nodes] (http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-4710)

Previously to show warnings on UI node, we add a property GUID to build/runtime warning entry so that a warning is associated with the corresponding UI node, but this granularity is still to big because a UI node may contain multiple AST nodes, for example, code block node. 

A new field ``AstID`` is added to build/runtime warning entry so that we can trace back to the corresponding AST node. 

@junmendoza , please review the change. Thanks.