Extend property tracker for abstract types

[Horusiath]

Currently property tracker has 2 cases:

• Direct (for tracker leaf nodes)
• Compose (for nodes with children).

The problem here may be how to deal with conditionally tracked properties (using GraphQL abstract types) - they are represented as tree of possible types and their field mappings in ResolveAbstraction execution plan part, but so far they don't have a correct equivalent in property trackers.

Idea here is to add two additional property tree cases:

• TypeDependent (wrapping other tree node with additional type condition)
• Inconclusive (special case, when we are no longer able to construct a property tracker due to i.e. node being passed to a method call that cannot be introspected)

/cc #100