Summary:
I was running flipper-server on a fresh machine without Flipper installed and discovered that reading / writing settings failed since `~/.flipper` wasn't existing, due to using `access` instead of `pathExists`.
Added a warning about needing to restart the server after making changes, since that is tricky to do from the UI.
Fixed an issue in the settings screen, which would fs.stat as part of rendering, causing the Settings UI not to load.
Reviewed By: timur-valiev, aigoncharov
Differential Revision: D32984538
fbshipit-source-id: 2b2011ad9d84c72ac824d92a8c96f636237b8771