Support for directions and direction flipping

Submitted by Tristan Van Berkom @tvb

Link to original bug (#387164)

Description

Gtk+ allows for complete flipping of the order of widgets in right-to-left language environments.

We should add some kind of support to let the user know what parts of their UI will be "flipped" around in an rtl language.

Parts of the UI that should not be flipped need to set thier "direction" manually I think (need to look further into this).