Refactor axis data. Remove duplicate paint code

[Cuteivist]

Changes:

• Added AxisData to place all axis data in one place and calculate range there. That will allow to easily add x axis.
• Moved calculating delta inside AxisData, so it is done only once when min and max are calculated.
• Changed way Y value position is calculated. Instead of calculating vStep it is using actual value difference. Reason for that is to be able to draw float ranges and reversing Y axis in future.
• Added property to enable or disable drawing points in line chart.
• Added property for line width in line chart.
• Removed duplicated code for painting lines in lines chart and vertical bar chart.

[fralx]

Hi! Thank you for your contribution to my project. I have tested your pull request and found that axis values are out of the item's boundaries Check it, please.

[Cuteivist]

@fralx Good catch, I will check item boundaries next time. I pushed fix for that.

[fralx]

Thanks