Getting Navmesh and work better with sublevels to update in 4.19

For those who want to put NavData into sublevels, check these configs:

UNavigationSystemModuleConfig::bAutoSpawnMissingNavData
UNavigationSystemModuleConfig::bSpawnNavDataInNavBoundsLevel

UNavigationSystemV1::bAutoCreateNavigationData
UNavigationSystemV1::bSpawnNavDataInNavBoundsLevel