More options to colorize tab foreground

This removes configure option tab.fg and adds tab.fg.odd, tab.fg.even and tab.fg.selected. This allows to change font color for selected tab and like that. I was missing that feature as I like using dark unactive tabs with active one being blue. I hope this is a good pull request and I'm doing things right as this is my first time doing this. If I'm doing something wrong, please say it and I'll try to fix.