When the last user exits a room, show 'no users' to remaining room owners.
CommandManager now throws on unmatched command

b/c why should the chat room see invalid or mistyped commands?
Merge pull request #749 from philchuang/handle-invalid-commands

CommandManager now throws on unmatched command
Merge pull request #747 from cmaish/last-user-exit

When the last user exits a room, show 'no users' to remaining room owners
Updated to latest SignalR nightly
Merge pull request #746 from cmaish/master

Disable file upload on lobby and in closed rooms