Flatpak Support for Settings Sync #621

🐛 Describe the bug
A clear and concise description of what the bug is.

I'm using latest version of Fedora, having Visual Studio Code installed via Flatpak so the vscode config folder doesn't exist in ~/.config/Code but rather in ~/.var/app/com.visualstudio.code/config/Code/.

Sync fails with Error: ENOENT: no such file or directory, stat '/home/<USER>/.config/Code'

🌴 Visual Studio Code Version : 1.26.1 via Flatpak 🌴 Code Settings Sync Version : 3.1.0 🌴 Operating System : Fedora 28 🌴 Occurs On: Upload && Download 🌴 Proxy Enabled: No 🌴 Gist Id: Not available because of error.

📰 To Reproduce Steps to reproduce the behavior:

1. Install VSCode with Flatpak
2. Install Extension
3. Try to execute Upload/Download
4. See error

💪 Expected behavior A clear and concise description of what you expected to happen.

Fully functional sync of settings / asking for github token at first run.

📺 Console Error Log If applicable, add screenshots or paste the console log from developer console of VSCode.

https://gist.github.com/daviian/cac70b2232dd6837b796248c5b43beae

📺 Additional context Add any other context about the problem here.