Move predef/ files into engine/

Get rid of single-file engine/ subdirectories
Move tilesets/ palettes unrelated to individual tilesets into data/palettes/ (more from engine/colors.asm can be moved here too)

engine/color.asm

@@ -1,5 +1,4 @@
-PALPACKET_LENGTH EQU $10
-INCLUDE "predef/sgb.asm"
+INCLUDE "engine/sgb_layouts.asm"
 
 SHINY_ATK_BIT EQU 5
 SHINY_DEF_VAL EQU 10
@@ -500,7 +499,7 @@ LoadMailPalettes:
 	RGB 00, 21, 00
 	RGB 00, 00, 00
 
-INCLUDE "predef/cgb.asm"
+INCLUDE "engine/cgb_layouts.asm"
 
 Function95f0:
 ; XXX
@@ -2027,13 +2026,13 @@ Palette_b311: ; b311 not mobile
 	RGB 00, 00, 00
 
 TilesetBGPalette:
-INCLUDE "tilesets/bg.pal"
+INCLUDE "data/palettes/bg.pal"
 
 MapObjectPals::
-INCLUDE "tilesets/ob.pal"
+INCLUDE "data/palettes/ob.pal"
 
 RoofPals:
-INCLUDE "tilesets/roof.pal"
+INCLUDE "data/palettes/roof.pal"
 
 DiplomaPalettes:
 	RGB 27, 31, 27

engine/link.asm

@@ -2034,7 +2034,7 @@ Function28f09: ; 28f09
 	ret
 ; 28f24
 
-INCLUDE "engine/trade/animation.asm"
+INCLUDE "engine/trade_animation.asm"
 
 Special_CheckTimeCapsuleCompatibility: ; 29bfb
 ; Checks to see if your Party is compatible with the generation 1 games.  Returns the following in ScriptVar:

engine/printer.asm

@@ -1,4 +1,4 @@
-INCLUDE "engine/printer/serial.asm"
+INCLUDE "engine/printer_serial.asm"
 
 SendScreenToPrinter: ; 843f0
 .loop