Make the `up` and `down` methods of Stack logical
Make the `up` and `down` methods of Stack logical

... and also consistent with Columns.

Fixes #1251

tych0/qtile,qtile/qtile,soulchainer/qtile,tych0/qtile,zordsdavini/qtile,ramnes/qtile,qtile/qtile,soulchainer/qtile,zordsdavini/qtile,ramnes/qtile