Add support for add/remove newline before and after ObjC @interface/@implementation lines

Add support for add/remove newline before and after ObjC @interface/@implementation lines. For example:
```
@interface Foo : NSObject {
    int ivar;
}
@end
```
…becomes…
```
@interface Foo : NSObject 
{
    int ivar;
}
@end
```
and things like that. Unit test coverage included.



Improve typing of chunks in ObjC @interface/@implementation lines.
Admittedly, ObjC being largely whitespace agnostic, there could have been many more options
(i.e. nl before/after class colon, category name, superclass, protocol list) but this is the
option I needed, so it's the one I built.