wip 1
World: Defer end of map editing during conversion; cleanup

Wait until control has returned to the engine before signaling that
map editing has completed. Previously this was done as soon as the
map converter first signaled completion (meaning it had to wait for
the engine to finalize the map, build a BSP, etc...).

Also improved some log messages (the number of polyobjs was missing
from the map element info, standardized formatting).

Plus cleanup.