Refactor code that gets ref label color

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
To make ref label easier to read, draw white text if back color is considered dark

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Simplify remote branch label ref name for single remote repository

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Show local branch that has remote tracking branch in round rectangle

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
At the right of local branch, show its remote tracking branch first, before showing other branches and remote branches

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Simplify remote tracking branch label ref name

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>