Update JCEF/CEF, create new JCEF mirror, add Linux and macOS support, bump version to 1.30

[ds58]

I've spent some time learning the inner workings of CEF/JCEF and decided to update this project

Notable changes:

• Updated Chromium/JCEF, now based on Chromium 88
• Add macOS/Linux support
• Linux does not require setting any LD_PRELOAD or LD_LIBRARY_PATH variables
• New JCEF mirror "Ruinscraft MCEF Mirror" -- https://storage.googleapis.com/ruinscraft-mcef-mirror
• MCEF now stores JCEF binaries in .minecraft/jcef
• Removed the letsencrypt SSL cert injector, it's no longer needed
• Removed "at runtime java.library.path injection" which will break on later Java versions and was unstable on some systems, causing potential "white screen" issues

On Linux, the custom web scheme "mod://" is currently broken. Normal websites/YouTube videos, etc work fine though. On macOS, on the first launch, you must go to System Preferences->Security & Privacy->General Tab and allow jcef_app.app to run. You may need to relaunch the game after you do this

Maintains compatibility with the latest release of webdisplays

Linux Example (Fedora 33)

macOS Example (10.15 Catalina)

[ds58]

If there's any interest in this in the future, the mirror has changed. See https://github.com/ds58/mcef/releases/tag/1.12.2-1.32