Babel sandbox version comparison

Feature request for Sandbox.

**The problem:** is it useful to compare the output of babel between two different versions (i.e. 7.10.4 and 7.10.x)?

**Outputs that we'd consider for this feature:**
- comparing output for bugs
- code difference
- code size (for outputs)
- determine when a change was made
- making a history of how things have changed

**Design spec:**
1. Have an input box for the user
2. Have one output box for the babel version the PR was submitted in
3. Have another output box for another version of babel

- [ ] figure out npm alias
- [ ] be able to import 2 of the same pkgs with diff names
- [ ] figure out how to get 2 different outputs with the pkgs
- [ ] how'd we grab the version that's submitted in a PR (by default: it's latest version)
- [ ] how'd we support all the versions & load them quickly

**UI Design:**
- At the moment, it would be similar to what's available right now on [sandboxes](https://codesandbox.io/s/github/babel/sandboxes)

**Considerations:**
- Version conflicts might come up with having 2 different versions of babel