Convert the generatorOptions from the world

[joserobjr]

Is your feature request related to a problem? Please describe.
Worlds with generatorOptions setup currently have this setting ignored since #49 was closed.

Describe the solution you'd like
Have all possible vanilla settings converted to the best Nukkit string possible, so new chunk generations follows almost the same setting as the original world.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.