Improve data labels algorythms of showing

[ktvale]

Sometimes data labels are not shown on random areas of line charts even if there is space for them. It usually happens on first and last values of line and sometimes on upper side of chart. It is important to see the last date labels on charts specifically if it is the last period values(when x-axis is time or date formatted)

[nishalit]

We made some changes to the labelling algorithm so it always defaults to showing the first, last, highest and lowest points first. You can use the slider in the formatting pane to show more.