Support Multiple Layer Stacking Directions

[weissi]

FRLayeredNavigationController should have a small abstraction layer, which abstracts from the screen's coordinate system. So, the axis and the direction of the axis in which to stack the layer (currently X-Axis in positive direction) should be configurable. After building that abstraction layer, FRLayeredNavigationController should easily support Left-to-Right (X-Axis, positive), Right-to-Left (X-Axis negative), Top-to-Bottom (Y-Axis, positive) and Bottom-to-Top (Y-Axis, negative) directions.

Especially Right-to-Left is interesting for bidirectional and RTL languages, such as arabic.

The code quality of FRLayeredNavigationController should profit of this abstraction, too.

The implementation should not be too hard, I think. There has already been an issue asking about RTL stacking.