#350: Add a command to download a map via lobby chat

[alexlambson]

• Add a command to download a map by hash: /downloadmap HASH
• Allow users to specify a filename after the hash, e.g. /downloadmap HASH [2] My Battle Map
• Fix a bug where renaming unzipped map files would cause a crash if the .map filename already exists.
• Relocate the file renaming to occur after we check that the file was successfully unzipped.

Users and devs can find map IDs using this URL template http://mapdb.cncnet.org/search.php?game=GAME_ID&search=MAP_NAME_SEARCH_STRING

Issue: https://github.com/CnCNet/xna-cncnet-client/issues/350

[github-actions[bot]]

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