Refactor messaging system to allow more flexibility

[mdziekon]

Summary

Current messaging system is inflexible in terms of how the message arguments can be presented and transformed before presentation to the user. In certain cases, it leads to bugs like #99, where certain piece of the message is "hardcoded" in the sender's message.

The messaging system should be refactored so that every "system message" could be programmatically transformed before being displayed, based on "facts-only" arguments stored as message's arguments. For example, instead of persisting the label of "origin point type" (Planet / Moon), we should be able to store the type's identifier, and then, when the message is about to be displayed, transform that into appropriate label. Not only this will make this more flexible and resitant to bugs, but also may result in a bit of space saving (however, that might be negated by the persistence format, which will most likely change to just JSON; still, space savings are not a priority anymore, at least not that low-level savings).

Related issues or PRs:

• Certain system messages sent to other users during calculation use the "host" user's language #99