Add option to auto-stack&tile

[humdinger]

On ​the forums it was suggested to see if we could do stack and tile (S&T) without the use of the OPT key.

S&T would be done as always, just without having to hold the OPT key. The "de-coupling" would be done dragging a window by its tab with the right mouse button.

We'd have to see if this auto-S&T would result in frequent accidental coupling of windows, or if the colouring of tabs/borders is enough of an indication to move the dragged window a bit further if you don't want to S&T.

Esp. if it's not clear cut that this auto-S&T poses no problems, there could be a new option in the "Look & Feel" tab of the Appearance prefs.

A checkbox:

Stack and tile: [ ] Automatically stack and tile windows

with a tool tip: "Un-stack/tile by dragging a window by its tab with the right mouse button."

Or, if it turns out that either stacking or tiling is more problematic, two checkboxes:

Stack and tile: [ ] Automatically stack windows
                        [ ] Automatically tile windows

each with the appropriate tool tip.