corelib: improved default palette

- light gray instead of 2x dark gray
- add palette file for paint programs
- new sprite with default palette for graphbench

examples/default-palette.pal

@@ -0,0 +1,19 @@
+JASC-PAL
+0100
+16
+0 0 0
+255 255 255
+255 0 0
+0 255 0
+0 0 255
+0 255 255
+255 0 255
+255 255 0
+127 127 127
+160 160 160
+127 0 0
+0 127 0
+0 0 127
+0 127 127
+127 0 127
+127 127 0

examples/graphbench.pas

@@ -106,7 +106,7 @@ begin
 end;
 
 begin
-	readSpriteData('rocket.sprt');
+	readSpriteData('sprite-testcard.sprt');
 
 	InitGraphics;
 	startBench('points 200K');