Option to completely disable join/leave notification pop-ups on the UI

[MagicaJaphet]

Since it hasn't been suggested here yet, an option to disable this feature:

Mostly suggesting as it seems to cause Window users in particular issues when they have a different full screen tab open, it forces them to switch to the program.

[askmeaboutlo0m]

This is implemented now by letting you pick which notifications cause a popup like this in the notification preferences.

It's available in the continuous development release: https://github.com/drawpile/Drawpile/releases/tag/continuous

Thanks for suggesting!