Classical tabs are very dated. They are also a practical problem as you
get very limited in the numbers of tabs we can have, and how long the
text can be on them.
Switch to one popular modern model with a list on the left instead where
pages can be selected.
Let's separate TigerVNC specific things from stuff that could be part of
upstream FLTK. These are files that we would like to collaborate with
other FLTK users, so they are more liberally licensed and avoid using
TigerVNC specific things.