User changing HipChat name will lose all stats

[gnjack]

The lower-cased name of a user is currently used as the key for that player & their matches in the DB.
This was to ensure we can support players who do not have a HipChat account (so can't use HipChat user ID).

Could be fixed by adding a rename command, this would need to update the key whever it is used, including all match history for that user as the key in the foosbot-match-history table. Alternatively, some method of switching to generated user IDs, linked to the HipChat ID if available. This would still require a rename command for non hipchat users, but wouldn't need to rewrite all match history for that user as the key in the foosbot-match-history table would not change.