Have a config option to forbid having spaces in nicknames

# Why is this important?
On servers such as my own that means that people can impersonate staff and pray on new players.

# What would be the fix?
Implement a config option that when set to true would check if a nickname contains spaces and disallow it if so. For example:
```json
"disallowNicknamesContainingSpaces": true
```

## Post scriptum
Whilst you are at it you could make a banned word list.
