Pikachu/Eevee Mode

So some bits of this are untested, but the base starters are unaffected. I had to work a lot with the sprite limits so Oak's lab has been changed a bit.

This adds a Pikachu and Eevee "mode" to the game, allowing you to pick them as starters. When doing so, the Rival will always pick the opposite.

There are some glitches;
- Picking Charmander makes Blue erase himself from existence
- Picking from anywhere other than the front of the table may have odd results.
- Oak has to be shown in the lab at the start from now on for some reason; side effect of removing the dexes, there's definitely a fix for this.
These are from me not finishing the ball picking process - it was a little weird.

Parties based on starters have been updated but I had to cut out a lot of unused trainer slots.

Also the unused names were removed.

constants/pokemon_constants.asm

@@ -267,6 +267,8 @@ DEF NUM_POKEMON_INDEXES EQU const_value - 1
 DEF STARTER1 EQU CHARMANDER
 DEF STARTER2 EQU SQUIRTLE
 DEF STARTER3 EQU BULBASAUR
+DEF STARTER4 EQU PIKACHU
+DEF STARTER5 EQU EEVEE
 
 ; ghost Marowak in Pokémon Tower
 DEF RESTLESS_SOUL EQU MAROWAK