Improve speed

[robertaboukhalil]

• [x] Hide terminal until ready and show what it's doing - https://github.com/sandbox-bio/sandbox.bio/commit/2320328219f17e64858299715824ae3505e2bd39
• [x] Playground for terminal shouldn't have extraneous break lines - https://github.com/sandbox-bio/sandbox.bio/commit/d919452d41b5b90d31e15c1c08d11e75ee44d6d9
• [x] Preload .bin files in parallel - https://github.com/sandbox-bio/sandbox.bio/commit/e2bf7e212aad8782d1d7373c4fcb3ede90abc88b
• [ ] Rely less on setTimeout in src/stores/cli.js line 76 (500 ms timeout), line 180 (200ms timeout)
• [ ] Always preload common tools like ls, vim, etc for all tutorials
• [ ] Running sync; echo 3 >/proc/sys/vm/drop_caches clears the cache of which files have already been downloaded, so when type the same command, it will still make a fetch request! But it returns quickly because the asset was cached at the browser level. Any speed difference? Probably not significantly, only extra operations are buffer = new Uint8Array(buffer) and map[sha256sum] = buffer.