Add saved note into media library

[brogowski]

• Add image and thumbnail into steam userdata directory structure
• Edit screenshots.vdf file to include new image
• Refresh media library

[brogowski]

Refreshing is only done on steam process start.
Probably need to keep separate gallery for not imported notes (with sync icon)

[brogowski]

Use SteamClient.User.StartRestart to force restart and re-import for screenshots