Added support for non-camel-case variable code conventions

Not all people use the camel case format for variable. A popular code style is to use underscores in the variable names like ```variable_name```, but use a getter like ```getVariableName```. This is however not suported by the ClosureExpressionVisitor since it will just check for an accessor concatinated with the fieldname.

This adds an extra check so that this code style is also supported by the ClosureExpressionVisitor.