Add UniversalEvents

[Sygmei]

UniversalEvents are events that can be triggered / listened from any programming language to any programming language.

For now, when Lua triggers a custom event, it is of type sol::table and thus can only be used by Lua callbacks.

The goal would be to detect if there is different kind of listeners (Lua, Wren, others...) and if it's the case, convert the data for non-compatible listeners.

The exchange format could be a vili::node containing all the required data.