Make some hardcoded menu text colors editable by menu skins
Currently, some menu text colors are hardcoded and cannot be changed by menu skins. This branch replaces those hardcoded colors with new variables for the skinvalues.txt file:
- COLOR_TEXT (Main text color)
- COLOR_TOOLTIP
- COLOR_SERVERLIST_CATEGORY
- ALPHA_SERVERLIST_CATEGORY
Existing skins are not affected by these changes, because the default values are the same as the old hardcoded ones.