tmux: Display message if config was reloaded.
tmux: Rework status theme, esp. use new *-style options instead of *-fg, etc.

*-fg, etc. have beed deprecated with tmux 1.9.
tmux: Disable messages on activity.
tmux: Different style for pane borders.
tmux: Drop deprecated default-path option.

Maybe, I will need to figure out an adequate replacement for this.
tmux: Renumber windows if a window is closed.

Never liked the gaps and that newly created windows appeared between
existing windows in these gaps.