Summary:
1) moved "sonar/desktop/src" to "sonar/desktop/app/src", so "app" is now a separate package containing the core Flipper app code
2) Configured yarn workspaces with the root in "sonar/desktop": app, static, pkg, doctor, headless-tests. Plugins are not included for now, I plan to do this later.
Reviewed By: jknoxville
Differential Revision: D20535782
fbshipit-source-id: 600b2301960f37c7d72166e0d04eba462bec9fc1
