Invincibility updates

- You flash white while in invincibility
- Invincibility is not rainbow UNTIL you go above the initial timer.
- Increased visibility of the shield effect around invincible players.
- Invincibility sparkles have trailing afterimages.
- Disabled invincibility speed lines; they now use the normal speedlines but grey/rainbow. (The code/sprites will be used for something later.)
- Using invincibility adds time, instead of setting it.
- Player hitbox is finally bigger, to actually match the shadow size.