Maximize side of window by double-clicking border

[nkkollaw]

One thing I would always do in macOS that I think is very useful was to mouseover a window border so that it would show the arrow, and then double-click to maximise the window in that direction.

So, if a window ended up in the middle of the screen I would "select" the left border, double-click, and the window would resize so that there was no margin to the left.

I think this would be a great addition to Gala.