[File systems] Prototype objectives fs-01 to fs-12

[joenash]

This PR adds prototypes for objectives fs-01 to fs-05.

Known issues & notes:

• Replace fs-jetpack in fs-03, due to this bug
• fs-01 only accepts posix style paths. We likely want a helper to facilitate comparing windows style and posix style strings.
• There's a philosophical issue about how we want to teach about the different path styles, we may benefit from an objective that teaches that explicitly and asks users to enter one path in both styles. Perhaps an optional objective after fs-01?
• In objectives checking command history, we mainly check the last element in the history, assuming the command was the last entered command. I've added a helper for the last 10 commands as well. These were both arbitrary, open to other approaches.

[rmkubik]

RE: Philosophy on path styles

I would buy the argument we should teach both styles to both types of OS. Especially windows users stuck in a linux-y web world are going to run into this all the time and need to translate between the two.

RE: Last 10 commands:

We've done similar arbitrary constraints. I think it's fine! The the thing you should do is make that constraint explicit in failure messages. We did that in some Twilio content where we checked to see if you sent the correct text in the last X messages. But sometimes a user might have sent the message yesterday or whatever and not realize.

We should always try to share as much of our failure case data as possible! This helps advanced users debug and not-advanced users share more useful bug reports!

[joenash]

Up to fs-12 as of 57f25f2