Implement Mobile version of Files tab / sidebar

[ghalestrilo]

Requires #1528

This branch implements an <Explorer /> mobile component, which uses a <Sidebar /> modal component (new) as a modal. It also updates the logic of the useAsModal HOC to support components that require the ability to close themselves (like the sidebar).

• has no linting errors (npm run lint)
• is from a uniquely-named feature branch and has been rebased on top of the latest master. (If I was asked to make more changes, I have made sure to rebase onto master then too)
• is descriptively named and links to an issue number, i.e. Fixes #123

[catarak]

This also looks so good! It's really, really exciting 😄

The only thing I'm unsure about is the floating file button, and I'd like to try having it be one of the icons next to the console icon.

[ghalestrilo]

Nice! I moved it to the bottom bar, and improved a couple things there

[catarak]

This looks great! I'm not sure what changes i would add other than getting the dropdown button to do stuff, but that could be another PR I think.

[catarak]

I think this one is ready 😄