Changed AstFactory.java: Inserted the warning types from
NAME_ENVIRONEMENT_AST, etc. in the corresponding containers, e.g. in
ENVIRONMENT_AST.
Added code to elementsBefore(DetailAST) in EnvironmentAst.java
Added elementsAfter(DetailAST) in EnvironmentAst.java and refactored
this class.
Refactored AstFactory.java respectively added FIXME-comment
Added getLastLineNumber() and getLastSibling() in Ast.java