Ignore messages in certain channels or with certain prefixes

[samollari]

Per suggestion of @EarlJr53, Jay, and Bri

When there are game bots or whatnot in the server, people may gain levels quicker than normal if they use them often. We should add a way to blacklist certain channels or message prefixes from counting towards levels.
E.g.
config.json

{
  "levels": {
    "ignoreChannels": ["channel1", "channel2"],
    "ignorePrefix": ["!", "m!", "m.", "p!"]
  }
}

[samollari]

This should be updated so the bot doesn't immediately crash when ignorePrefix isn't defined (it should be optional in Types.ts and should be checked if it's defined before trying to use it)