Set smart_gaps on as default

[FilippoBonazziSUSE]

We have a suggestion in #141 to add smart_gaps on as a default. From man 5 sway:

smart_gaps on|off|toggle|inverse_outer
           If smart_gaps are on gaps will only be enabled if a workspace has more than one child.
           If smart_gaps are inverse_outer outer gaps will only be enabled if a workspace has exactly one child.

I do not use gaps at all, so I have no opinion on this.

[denisok]

-1
I tried it swaymsg smart_gaps toggle and for me personally aesthetic of a gap even on single window is better.

this setting could be easily enabled in personal config ~/.config...