Display MainGame.mnu and map in ordoor simultaneously

It's a complete mess for now - many things are out of place or shown
when they shouldn't be - and we can't move around the game map. But,
it's a good start.

doc/formats/mnu.md

@@ -245,13 +245,14 @@ observed, suggesting structure. For instance, we have `24`, `240`, `241` and
 `2410`, but not `2411` or `2409`. Sometimes we have a comma-separated list,
 e.g.: `400,30,-1,5`.
 
-A listing of currently-known values:
+A listing of some currently-known values:
 
 | Value | Type             |
 | ----- | ---------------- |
 | 0     | Static image     |
 | 1     | Menu             |
 | 3     | Button           |
+| 45    | Thumb            |
 | 50    | Invoke? Button?  |
 | 61    | "Overlay"        |
 | 70    | "Hypertext"      |
@@ -260,6 +261,13 @@ A listing of currently-known values:
 | 228   | Main menu button |
 | 232   | Slider           |
 
+Hypothesis: `MENUTYPE` and `SUBMENUTYPE` are actually distinct lists of values.
+So far, I've been treating them as the same thing, but, e.g., `MainGame.mnu` has
+a `MENUTYPE: 45` which is labelled "MAIN BACKGROUND", while `SUBMENUTYPE: 45`
+is tentatively labelled a "thumb" and used in text boxes. There are also a few
+cases where I've had to manually override the `MENUTYPE` because it coincides
+with `Button`.
+
 ### `ACTIVE`
 
 There are only 4 values seen across all menus: `0`, `1`, `1,0`, `102` and `1,1`.