Custom tick generation

Add functionality to provide custom tick generator for quantitative scale.

Close #1058.
I wrote this line based on other similar test case.
This line checks assures that we are using default generator, which should generate about 10 ticks. The result here is 11, even if we pass 10.
This is from d3 doc:
`The specified count is only a hint; the scale may return more or fewer values depending on the input domain.`
That's why we keep `closeTo` and probably 1 was empirically set.