Add support for sending custom markers from the game/engine

[XDargu]

Add the option to send custom markers from the client side. Maybe with some config? Like name and color, with some defaults.

[XDargu]

Also, perhaps add the option to add custom markets in Frame by Frame?

[XDargu]

This is now partially possible by using comments. It's not possible to create comments from the client, but it is possible to add them to an existing recording.