Improve UX when server fails to save changes

[MeoMix]

The entire program fails to properly convey failures from the server. If saving a playlist title fails... no message. If saving an item fails... loading spinner spins indefinitely.

I think a full audit of the code is in order. A few steps are needed:

• Locate all points where communication with external servers occur. This includes YouTube's API.
• Ensure that error callbacks are attached to all such calls.
• Ensure that the UI conveys errors appropriately.

Bonus points:

• Use desktop notifications to convey errors when main UI is not available.
• Allow the user to retry.