Autorotate discrete

[RYangazov]

The behavior of jitter and jitter_dodge changes when the orientation is altered.
Even when the seed value is set, the distribution of geom_point() isn't maintained.

This is due to JitterPos.translate applying random coefficients to the coordinates in a different sequence.
This kind of behavior is also seen in ggplot2

[alshan]

IMO it should be done differently.

1. There should be a function which inspects layer's geom/stat and defines if "orientation" is applicable to the layer. For example, true if stat "count", or true if geom "bar".

2. The decision about layer's orientation should be done only at the "backend", before stat is applied.

3. If concluded that orientation is "y", then add option "orientation=y" to the layer's options (see fun replaceOwnData() for example).

4. If only aes Y is mapped, then orientation is definitely Y.

5. If both aes - X and Y are mapped, then check whether the Y is discrete (mappings, data). And no need to combine dataframes to perform this checking. However, if X is discrete, then no need to check Y.