Unknown options get overwritten

The Bug

When switching between versions, the newer version always overwrites unknown options in the options.txt. This could be fixed by ignoring unknown keys and keeping them as they were before.

How to Reproduce

1. Open the game in 1.15.2 (or newer)
2. Enable toggle Sneak
3. Open the game in 1.14 and open the settings without changing anything
4. Launch 1.15 again
   → The option resets to the default value