Add: Rudimentary handling of map/layer properties
Ref: Re-name property "properties" to "attributes"
Add: Map parser scope, map/layer attributes

The parser maintains a stack of scope objects that can be used to
perform scope-specific actions.
It has been introduced to assign parsed attributes to the
correct object in the map hierarchy.
Add: Parser scope test, OCMock for mocking
Rem: Isometric map layout test