Fixes and adjustments for character select menu

[Daniel-Cortez]

This PR does the following:

• Fixes X and Y inputs overlapping when ↑/ ↓ and ←/→ buttons are pressed at the same time. How to reprocuce the bug:
  1. In Character Select press and hold the → button. Currently selected character will switch forward from "Sonic and Tails" to "Sonic".
  2. Press the ↓ button (while still holding the → button). The level will switch to "Base Zone Act 2", but since the → button is still being pressed, the character will also switch to "Tails", as if the button was released and pressed again.
  3. Release the ↓ button (with the → button still being pressed). The character will again switch to "Knuckles".
• Minor cosmetic fixes for more polished look:
  • Use named constants for character IDs, as hardcoding them isn't a good practice.
  • Improved centering of character sprites on the screen. I had to duplicate Sonic's and Tails' sprites for this (one pair of sprites for "Sonic and Tails", and the other for "Sonic" and "Tails" alone each; copied Tails' tails too), as changing their coordinates via scripting (and hardcoding their coordinates in the code) wouldn't look as good. This also allowed me to remove some repetitive code.
  • Play switch sound when changing character and level selection.

[Caverns4]

One small bug: When releasing the input after pressing up or down on a controller's thumbstick, the switch sound plays twice. Please try to fix that if you can, and then this will good to pull.

[Daniel-Cortez]

Yeah, not only that, but the line for playing the sound when pressing ←/→ is missing too... Guess I accidentally lost that line when I was porting the corresponding commit from an older local branch (I originally did that one change back in July, when the code for handling inputs was different from how it is now).

Anyway, both problems should be fixed now.