Update completion status directly from Playnite Web

[andrew-codes]

I'd like to be able to update a game's completion status directly from Playnite Web. Game data should be reflected as updates in Playnite.

Some considerations:

• What if I update a game and Playnite is inaccessible at that time? These updates need to be applied as soon as possible to Playnite once it is accessible.
• Update mechanism should only allow me to update to valid completion state values.