Don't report unused parameters when method has an IBAction attribute

When working with Interface Builder and connecting UI elements the the source, the method signature is always something like this:
```- (IBAction)methodName:(id)sender;```
The method parameter is mandatory; Interface Builder insists on this. In most cases the ```sender``` isn't needed but the unused parameter is reported by OClint.

This change adds a check to the ```UnusedMethodParameterRule``` that prevents reporting the violation if the examined method is an ```IBAction```.