Is your feature request related to a problem? Please describe.
SWM is checking for level.dat file when checking the integrity of a map but it is not really necessary to have that file to get a world working in vanilla. In fac I don't use level.dat on my BedWars1058 and I just noticed that they can't be loaded because they are required in SWM.
Describe the solution you'd like
We should make it optional, If the file is missing we should create a default LevelData which is also almost useless when we set x,y,z using the API, and since level.dat contains the DataVersion we can retrieve it from a chunk.