* Changes delegate property from assign to weak

In modern Objective-C delegate should be weak. In very rare conditions you might want delegate be strong.
Assign for delegate is sign of legacy code.
This change prevents crash when you forget nil delegate in dealloc and makes rush with nilling delegate unnecessary.
This change shouldn't break any existing code.

* Adds implementation for setters and getters for weak delegate properties for non ARC Obj-C files

For whatever reason compiler can't synthesize these.
And yes, it's time to convert all Objective-C stuff to ARC.