Make Task History chart more sane
Make Task History chart more sane

Change the chart type to standard line (no weird steps) so that
all the lines can be tracked clearly, rather than all same-day
changes overlapping each other in one vertical line. Also use
shared tooltip so that information for multiple tasks with the
same number of hours remaining are visible simultaneously.

mrozekma/Sprint,mrozekma/Sprint,mrozekma/Sprint