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

[ericalloyd]

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