Finish Chief, bug fixes

This finishes Chief's event, with all the necessary components for the post-game Mewtwo fight sorted as well. I added an event the Master Ball sets for modular monologue text, for improved immersion.

I have also fixed some bugs;
- Fixed the oft-reported walking in trees bug in the Forest tileset.
- Fixed the Oak's lab computer issue by just...removing the computer. I made the map symmetrical instead, feels a lot better to look at, at least for me. I think it was meant to have an event on it or something, but I couldn't find anything, felt like I was being gaslit.
- Hopefully fixed the issue with the border blocks going weird after saving and resetting, by making the tileset directly point to the gym one, which Oak is meant to use. I am not sure how that glitch happened for ViWalls.
- Fixed the Viridian Pre-Gym text scrolling issue.

I still cannot replicate the crash bugs that some people have been experiencing and don't see anything that could be causing it.

I also changed Trampel in Victory Road to Steelix, as mentioned by Gogocrafter.

data/maps/objects/SilphGauntlet7F.asm

@@ -2,9 +2,12 @@ SilphGauntlet7F_Object:
 	db $d ; border block
 
 	def_warp_events
-	warp_event  5,  6, SAFFRON_CITY, 1
+	warp_event  5,  6, SAFFRON_CITY, 9
 
 	def_bg_events
+	bg_event  2,  2, 2 ; Chief's PC
+	bg_event  2,  0, 3 ; Chief's first painting
+	bg_event  8,  0, 4 ; Chief's second painting
 
 	def_object_events
 	object_event  5,  1, SPRITE_SILPH_PRESIDENT, STAY, DOWN, 1 ; person