Use schematic in dig, interpret the schematic in schematic_helper

## Type of Issue

Select the type of issue:
- [ ] Bug report (to report a bug)
- [x] Feature request (to request an additional feature)
- [ ] Tracker (I am just using this as a tracker)
- [x] Refactor request
- [ ] Documentation Ask

## Description

Right now the set of blocks to be removed is interpreted partially in handle_dig in mc_interpreter and partially in the Dig Task. Change Dig task to take an explicit schematic in its task_data (instead of height, width, etc.), and interpret the schematic in schematic_helper.py