Add option to "recreate all" for conflict and games repo creation

When running the script to create `conflict-practice` and `github-games` repos for students based on the day 1 repo collaborator list, we should have an option to recreate repos for **all** students without stopping after each one to ask for input:

```
Is it OK to delete and recreate? [y/N]
```

Example:
```
⇒ script/teach-class --recreate-all
```

An alternative would be to add additional options to the selection menu:

```
What would you like to do? (Just the number please)
99: Exit
0: Confirm setup
1: Create a new caption-this class repository
2: Add collabs and create files (also makes the repo private)
3: Grade the day 1 repo
4: Create conflict repos for each student
4a: Recreate all existing conflict repos for all students
5: Grade the conflict repos
6: Create the github-games repos for each student
6a: Recreate all existing github-games repos for all students
7: Delete student repos for a specific class
8: Grade client
6a
```