Simplify tileset-specific sequence definitions.

All magic behaviour for constructing sprite filenames
has been removed in favour of an explicit Filename
(and TilesetFilenames for tileset-specific sequences)
property.

mods/d2k/sequences/aircraft.yaml

@@ -1,23 +1,28 @@
 carryall:
-	idle: DATA.R8
+	idle:
+		Filename: DATA.R8
 		Start: 1923
 		Facings: -32
-	icon: DATA.R8
+	icon:
+		Filename: DATA.R8
 		Start: 4290
 		Offset: -30,-24
 
 ornithopter:
-	idle: DATA.R8
+	idle:
+		Filename: DATA.R8
 		Start: 1955
 		Facings: -32
 		Length: 3
 		Tick: 120
 		Transpose: true
-	icon: DATA.R8
+	icon:
+		Filename: DATA.R8
 		Start: 4292
 		Offset: -30,-24
 
 frigate:
-	idle: DATA.R8
+	idle:
+		Filename: DATA.R8
 		Start: 2517
 		Facings: 1