Feature request: File upload progress indicator and pause/resume

For large file uploads, it would be very useful know how much data has been uploaded so far, and to be able to pause/resume. Pause/resume are useful in any app where users may be uploading many gigabytes at once, but especially so in Keybase since uploads consume CPU, not just network resources.

I'm on the Windows desktop app version 4.5.0-20190919000314+93e889ab01, in case that's helpful to know.

The issue names no files, tests, or entry points. Start by locating the desktop app's large-file upload flow and its existing upload state handling; done means users can see upload progress and pause and resume large uploads.

Written by the indexing model from the issue text.