qchart axis enhancement

QValueAxis and QCategoryAxis automatically change axis labels to something like "23.." or "..." if number of ticks is larger than 15 or 20.   It is not the right way to reformat the tick label on the basis of number of ticks.  It is because if the chart window is large, there is enough space to display large amount of tick labels.   The correct way is to check the space between ticks.

QCategoryAxis only takes unique labels.   If the label already exists, it will be ignore.  Duplicate labels should be allowed.   Axis is used to display a label.  The label can be anything.  It does not have be unique.       One example is timestamp.   Because QDateTimeAxis does not support discrete timestamps.  Users have to use QCategoryAxis. Users can print timestamp as "Month/Day/Year", "Month/Day",  or "Hour:Minute".  Even though timestamps are all unique, there can be duplicate labels.  Users may choose to print year only when there is a year change between ticks.  

It would be nice to add an index to QCategoryAxis so that each label can customized individually.  The index will the index of the data series.