[SDL-0007] - Migrating to Generics for Collections

[asm09fsu]

Bug Report

This issue is related to Proposal 0007 - iOS Enforce ObjC Generics.

From the Motivation:

The SDL iOS library has many public APIs that expose a collection class (array, dictionary, set, etc.), for example, RPCs do this all the time. Before Xcode 7, these collections had to be untyped. However, since Xcode 7, we are able to use "lightweight generics" to expose what, exactly, we expect the collection to contain. These are lightweight because they are not enforced by the compiler except through warnings in Objective-C. However, these generics also translate to Swift apps which integrate the library as compiler-enforced generics. This will not only vastly improve Swift compatibility, but will also improve our indications to Objective-C developers what we intend.

[asm09fsu]

Duplicate of #247