Added an option in the configuration to change the height between buttons.
IMPORTANT: This may cause the buttons to change their position on the screen, so you must use the SPECIAL_THEME configuration to adjust the height. You'll have to add values for both the BUTTON_HEIGHT (for the default pokegear menu) and THEME_BUTTON_HEIGHT (for the pokegear theme selection menu) but you can simply put the default height to keep the buttons where they are if you didn't make changes for the corresponding menu.