Infrastructure: Replace electron-download, improve download experience

We’re currently using electron-download. This has benefits: We’re now that we’re always downloading the “right” Electron binary and can simply pull in its latest version to get the same behavior as npm i electron.

But it also has downsides:

• electron-download constantly prints to stdout, creating quite a bit of unnecessary work when used as a library
• It comes with dependencies that need resources but end up not benefiting the user experience
• We currently can’t get the progress of the download

We should either improve electron-download to the point where it can be properly used as a library or replace it entirely. Improving is probably the better path but it might require splitting electron-download into multiple packages.

cc @MarshallOfSound

[malept]

As well, allow the download to be cancelled by hovering and clicking on the same area.

I’ll need to think about how we can expose download cancellation so we can resolve #320. It seems problematic with the current implementation because we’re using stream piping to write the HTTP response to a file.

[erickzhao]

@malept Would probably be ideal to show progress using a Blueprint.js component in the Version Select right where the “Downloading” text is right now. As well, allow the download to be cancelled by hovering and clicking on the same area.