Improvements in Logit scale ticker and formatter

Introduced in version 1.5, the logit scale didn't have appropriate ticker and

formatter. Previously, location of ticks was not zoom dependent, too many label

was displayed implying overlapping which break readability, and label formatting

was not precision adaptive.

Starting from this version, the locator have near the same behavior as the

locator for the log scale or the same behavior as the locator for the linear

scale, depending on used zoom. The number of ticks is controlled. Some minor

labels are displayed adaptively as sublabels in log scale. Formatting is adapted

for probabilities and the precision is adaptive depending on the scale.