Proposed text-based "advanced mode" events editor for QtFRED

FRED's traditional hierarchical menus for creating and modifying mission events is great for making sexps discoverable and accessible to newcomers, but for people who already know many sexps, all the hunting and pointing and clicking and having to remember where the sexp you want is located in the menu system is a huge drain on productivity, much like many other "friendly" graphical interfaces for largely text-based tasks. Since QtFRED is a comprehensive rewrite of FRED, now is the time to consider an alternate event editor--a _text editor_, with which you would write events, manage variables, etc. the same way you would write the Lisp code that FreeSpace sexps are inspired by. Such an editor could be specially tailored to the needs of FreeSpace events, with syntax highlighting and keybindings for common tasks, and sanity checking to prevent passing garbage data to the other parts of the editor. This could greatly streamline mission design for intermediate and advanced users and eliminate what is probably the most boring and tedious part of using FRED.