Things to change for a protocol v2

I'd like to start keeping track of things we want to change in a new protocol.

### Stuff to remove
- [x] Remove `QDataStreamProtocol` #816
*It is pointless, everyone hates it.*
- [x] Remove all modvault functionality #816
*Only the legacy client still uses it. All clients should use the API instead.*
- [x] Remove `create_account` command completely #816
- [x] Remove `id` and `login` from the welcome message. #816
*Use corresponding attributes on the `me` object instead*
- [x] Remove `mod` from `game_matchmaking` command. #816
*Use `queue_name` instead.*
- [x] Remove `faction` from `game_matchmaking` command. #816
*Use `set_party_factions` instead.*
- [ ] Remove password based authentication
*Use token instead*
- [x] Remove `init_mode` from `game_launch` command. #816
*Use `game_type` instead.*
- [ ] Remove `kick` and `kill` styles from notice messages
*Use a dedicated administrative command instead*
- [x] Remove search boundaries from `matchmaker_info` message #816
- [x] Remove `irc_password` command
*IRC authentication will use tokens from the API*
- [ ] Remove `global_rating`, `ladder_rating`, and `number_of_games` from `player_info` message.
*Use `ratings` instead*

### Stuff to change
- [ ] Rework `command_avatar`
- [ ] Rename action `list_avatar` to `list`
- [ ] Return avatar id's in avatar list
- [ ] Select avatar via id instead of url
- [x] Move from UTF-16 to UTF-8 #629
*We are just wasting bytes*
- [ ] Move the protocol to websocket, choose a websocket subprotocol (e.g. STOMP?)
*This would allow more web interactions*
- [ ] Guarantee that every message is a json dictionary (not a list)
*Simplifies parsing*
- [ ] Change all unix timestamps to ISO timestamps. For example `launched_at` in `game_info`
- [ ] Remove or rework `ping` and `pong` commands? Maybe only send them if no other messages have been sent
- [ ] Rework `game_info` so that messages are not sent sometimes as a list and sometimes as individual games
- [ ] Use player id instead of username in `game_info` teams section #812
- [x] Don't send `game_launch` message when match is cancelled #816
*Handle `match_cancelled` instead*
- [ ] Rework `command_ask_session`
*What is the point? What does the policy server use this for? Can it be removed?*

### Stuff to add
- [ ] Add message Id to every message (or a message envelope)
- [ ] Add request Id to messages that are a direct response to other messages.
- [x] ~A way to tell when a player has left an ongoing game (player dies but game is not over).~ #831
- [ ] Matchmaker match confirmation #607
- [ ] Add a way to check supported protocol version of clients

### Fancy features
- [ ] Auto-generate documentation or describe protocol in a formal language that allows creation of code in multiple languages
*Use dataclasses to describe message fields*