sprites: improve player back walk animation

The legs were reworked as well, matching the changes done to the front.

The shoulder pads movement was toned down, and the left arm was changed
so it's movement is a bit less abrupt and can actually be followed.
Other minor tweaks and size was made proportional to the front frames.

buildcfg.txt

@@ -2333,22 +2333,22 @@ PLAYA1	22	52
 PLAYA2A8	16	52
 PLAYA3A7	21	50
 PLAYA4A6	23	49
-PLAYA5	19	47
+PLAYA5	24	53
 PLAYB1	19	53
 PLAYB2B8	18	52
 PLAYB3B7	19	52
 PLAYB4B6	21	52
-PLAYB5	18	51
+PLAYB5	20	53
 PLAYC1	20	53
 PLAYC2C8	16	51
 PLAYC3C7	18	51
 PLAYC4C6	22	51
-PLAYC5	17	50
+PLAYC5	21	52
 PLAYD1	19	52
 PLAYD2D8	17	52
 PLAYD3D7	19	52
 PLAYD4D6	23	52
-PLAYD5	19	51
+PLAYD5	24	52
 PLAYE1	12	51
 PLAYE2E8	21	51
 PLAYE3E7	26	50