Tutorial: Adding a resource

In this tutorial I'm going to list the steps taken to modify the domain and relevant parts of MIDCA to add a resource into blocks world: mortar. The essential idea of mortar is that it allows building more "stable" towers. Mortar can be applied in between two blocks during a stack operation, and can be removed during an unstack operation.

Steps taken:

1. change the planning operators and methods relevant to the new resource: here we change the stack and unstack operators, as well as the put method.

2. change midca's worldsim files (midca's representation of state and the domain) which are located in the worldsim module.

3. next change the function that converts midca's world state into a state used by the planner. These are the functions 'pyhop_state_from_world' and 'pyhop_tasks_from_goals' located at the bottom of modules.planning.py