Some minor fixes

I hope this pull request is cleaner than the first one, it contains only minor fixes:
 * Modifies the multiplayer kart selection so no player is autoselected at the beginning
 * Deactivate checkboxes in the custom video settings screen to make possible settings more obvious
     * I slightly changed the way deactivated spinners are handled (this time in a better way) so the original text is not drawn above the '-'
 * The I18N tags are more unified in the screens and I also changed the indention from 6 to 8 spaces in one file (there shouldn't be other changes, only diff doesn't notice the indention changes properly)