feature: Comparator Nodes

[kimsanbaev-karim]

Comparator feature. A comparator takes values from two child nodes and compares them. Usage examples: Calculating the distance between two objects. Any arithmetic operations.

This also includes Getter nodes. They fetch objects and classes from the external world. Usage examples: Fetching the player object to later check the distance. Set and Get variable to/from Blackboard Since the blackboard doesn't allow linking references from outside, and since the entire tree gets duplicated, resulting in a 'Type mismatch' + blackboard cannot be viewed during execution, Getter nodes solve this problem.

[kimsanbaev-karim]

Pull request https://github.com/luis-l/BonsaiBehaviourTree/pull/30