Use "angle" instead of "direction" for text

[GravisZro]

This replaces all instances of direction/setDirection with angle/setAngle for the DrawText type. Internally a QTransform is also stored so that the transform matrix doesn't have to be continually recalculated on every paint event. This also more closely matches the KiCAD file format which also uses a numerical value for the angle.

Testing is needed before merging.

[sebcaux]

I agree with angle instead of direction (direction was the term used in kicad 4 model), but the transform should not be place into model.
Tranform should be moved internally in DrawTextItem.

[GravisZro]

Moving the QTransform into the DrawTextItem is ugly (requires adding a signal for when setAngle is called) so now it's merely calculated ad hoc.