Simple support for to handle differents icons with backward compatibi…

[lo-g]

My goal was to have differents thumb images.

For to reduce at minimun check against all provided icons (normal, disabled, presses) for both thumbs, I thought to proceed in the following way:

1. If thumbNormal is provided -> everything works normally as now
2. if thumbNormalLeft AND thumbNormaRight are provided AND they have same dimensions -> set different icons.
3. if dimension of thumbNormalLeft and thumbNormaRight are different -> fallback to default case with default assets.