Factory methods for instantiation, removed ArrayAccess

What's Changed

• BC BREAK - Require item class name to be provided via abstract method getItemClassName() instead of via the collection constructor.
• BC BREAK - Removed support for ArrayAccess, and replicate functionality via more meaningful methods such as Collection::has() and Collection::get().
• BC BREAK - Collection::toArray() renamed to Collection::all().
• Added the factory methods Collection::from() and Collection::empty().
• Added helper methods Collection::isEmpty() and Collection::isNotEmpty().
• Added helper method Collection::mapTo() to map to a new Collection of a different type.
• Added Collection::reverse() helper to reverse the order of the collection.
• Support creating collections from Doctrine Collections using Collection::fromDoctrine().
• Support creating collections by mapping array of other objects using Collection::mapFrom().