Enable points mode category axis

Enable "points" mode in Axis.Category and add test that verifies range values in different range type.
Add update range after setting range type.

Close #919.
@danmane He already added the unit test.

@bluong Technically out of scope based on the bug filed, although basically `rangeType()` doesn't work properly at all unless he fixes this (you couldn't change the padding after rendering for example).