[desktop] Basic electron app

Summary:
This diff adds a basic desktop app setup.

• it's contained in the desktop workspace
• desktop/pages contains code for the splash/ loading window and connection error window
• desktop/forge.config.js is a configuration for electron-forge whish is a packaging helper

Test Plan:

• Run yarn dev in keyserver and web. Run yarn dev in desktop and check if it works in developement
• Run yarn make and check if resulting executable works with production server

Look for any differences with the web browser version.

Reviewers: tomek, atul, abosh, kamil, ashoat

Reviewed By: tomek, atul

Subscribers: jon, kamil, ashoat

Differential Revision: https://phab.comm.dev/D5629