Start decompiling overlay 74 (main menu + other things)

[tgsm]

A lot of documentation still needs to be done, but it is decompiled :^)

[adrienntindall]

Ideally this could use some work on the documentation end since a lot of the variable names right now are incredibly messy, at least add in message contents as comments and do what you can using those

[adrienntindall]

Ideally whenever we use a message const, we should add a comment next to it with its contents (mostly so the code can be understood easier and better documented)