Update examples_and_tutorials with changes introduced by refactor

## Type of Issue

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

## Description

Our examples and tutorials are based on an older state of the repo. The recent code refactor and redesign of subsystem logic has been breaking those (or at least making them outdated). We should take a pass on all files under `examples_and_tutorials` and bring them up-to-date.

I'll take a pass on the grid agent example `examples_and_tutorials/grid/` and `examples_and_tutorials/tutorials/how_to_build_a_simple_agent.ipynb`. @soumith could you take a pass on robot side?

## Current Behavior

Some of the examples and tutorials are broken/outdated.

## Expected Behavior

Bring all files under `examples_and_tutorials` up-to-date.

## Checklist

Use this checklist if you are using this issue as a tracker:

- [ ] `examples_and_tutorials/grid/*`
- [ ] Task 2
- [ ] Task 3 ...