Resolve issues and remove `-nographics` flag. 🔥

Changes:

• #261 Remove -nographics flag, ensure single -batchmode flag*

*requires game-ci/docker image >= 0.13 (builder uses latest 0.x automatically by default)

What does this mean?

• ✅ Global Illumination (GI) system can be used again in all versions.
• ✅ Full legacy render pipeline support
• ✅ Full URP support
• ✅ Full HDRP support
• ✅ Many seemingly random crashes have been resolved

Except for the following versions which are hereby deprecated:

• ❌ 2020.1.0f1 ~ 2020.1.5f1 (6 versions)

Credits:

Thanks to everyone who helped out determining the cause of several different issues.