Notify Playnite user on failure to authenticate or sync library

[andrew-codes]

Currently, when opening Playnite, the Plugin attempts to either authenticate or use a prior authentication. However, upon failing to authenticate, there is no notification to the user. Furthermore, performing a library sync will also fail, due to authentication, and again there is no feedback to the user to indicate there is a problem.

Update the Plugin such that failures to authenticate produce a notificaiton in Playnite's notification pane. Additionally, failing to sync should also produce a notification in the same manner. Each of these two notifications should use verbiage that communicates the nature of the failure/error that occurred.