GStringExpressionWithinStringRule should ignore quasi GString expressions inside annotations

Currently GStringExpressionWithinStringRule reports violations when quasi GString expressions are used as elements in annotations. 

It's not good for two reasons:

a) Frameworks such as Spring use similar syntax (http://stackoverflow.com/questions/5648398/using-value-spring-annotation-with-groovy). If project uses Spring, developers actually need to put such expressions inside single quote Strings (otherwise it will not compile - see below)

b) Double quote Strings with ${} expressions are not allowed in annotations (groovyc will not compile it).