Grow/Shrink Bindings

[ssokolow]

It should be possible to grow/shrink windows horizontally or vertically by some small increment (10px?) using the numpad /*-+ keys.

To do this properly will require window gravity (Issue #9) and some mechanism to remember gravity for a given window as assigned by the last tiling operation but invalidate it and reset to some user-specified default on manual repositioning.

Maybe a dict with native window IDs for keys where the values include the last quicktile-set geometry as a validity test.