Support hidden names sessions with names start with a '_', adding in the process support for tmux hidden sessions whose names can't start with a '.'.
* usr/lib/byobu/include/select-session.py:
  - This branch adds named sessions starting with an underscore also as
    hidden sessions in alternative to named sessions starting with a dot,
    since tmux doesn't support session names starting with a dot. In the
    process it also adds support for hidden session in tmux if the
    session names start with an underscore, adding this feature to tmux
    based byobu.
* usr/bin/byobu-layout.in:
  - add a list-layouts command