exportlegends includes new maps

I modified `exportlegends.lua` to also export the new maps (`Nobility and Holdings`, and `Diplomacy`).  

I also found but couldn't work out how to fix a bug - regardless of whether the argument was `maps` or `all`, the maps were exporter but the other information was not (legends XML, text files, tile map.  
This should probably use `#MAPS` instead - is there a reason for zero-indexing MAPS? (`#` starts at index 1, so if this needs to be zero-indexed, you should use `if i <= #MAPS`)