Make our own shell-like environment

Having our own shell would allow us to see user input, so we could track whether they have run certain commands.

We could track things like:
- `git revert`
- `git reset`
- `git cherry-pick`
- `git diff`
- `git remote`
- `git config`
- `touch`

Other pros:
- Switch to fake git users when simulating remote interactions
- Set the colors of the terminal, show branching information inline
- Log user commands so they can ask for help (#167)
- Automatically track progress
- Tell the user what to do
- Feels more like a videogame
- Have much more flexibility when creating levels
- Change contents of files on the fly
- Automatically use the newest version of git

Cons:
- Maybe confusing to users
- Probably slow
- Probably buggy
- Definitely time-consuming
- Definitely privacy issues