Seamless Loading Screen

What's New?
- Now takes a screenshot when you close the window instead of only when quitting to title
- Added the ability to use custom screenshots for servers¹
- Added option to also update singleplayer world icons
- Fixed bug when changing dimensions
- [Internal] Simplified the screenshot taking process
- Attempts to fix crash on exiting a realm²
- Attempts to add full support for reams²

¹: To do so, join and leave the server at least once, then go to `Edit Server` and turn on `Custom Screenshot`. Afterwards, go to your screenshots folder -> worlds -> servers, copy the file name for the server, delete the old file, and put your custom image/screenshot there with the name you just copied from.

²: I am unable to really test out realms much, if I missed a screen or if the crash still happens, open an issue in the github repo.