Improvements for Axis: 1. for rotated labels align the label's corner at the position of the tick 2. use spin boxes to specify the tick increment for numeric and datetime formats 3. when switching between the "number" and "increment" options for the number of axis ticks for the first time, preserve the number of ticks to avoid the unwanted big number of ticks as it was in the past when the increment was set to a small value

Differential Revision https://phabricator.kde.org/D18476