Workaround for rendering issue with doji candles #623

[lauxjpn]

Workaround for rendering issue with doji candles (candles with bodies so small, they are just represented by a line). It seems that WPF falsely renders these rectangles with their left coordinates adjusted to the left by the rectangles width (which effectively draws a line double it's intended size). In these edge cases, let's just draw a line (or two) instead of a polygon.

This issue was addressed here:
https://stackoverflow.com/questions/33130300/oxyplot-candle-overlap-each-candle

It might also fix #623 (hard to tell, because the images of the issue are missing).

Before the fix:

After the fix:

Checklist

• [y] I have included examples or tests
• [y] I have updated the change log
• [y] I am listed in the CONTRIBUTORS file
• [y] I have cleaned up the commit history (use rebase and squash)

@oxyplot/admins

[lauxjpn]

Just saw a brand new reported issue regarding this fix, but in the other series:

CandleStick is overlapped when item.open == item.close in the CandleStickAndVolumeSeries #1245

[lauxjpn]

I provided a new pull request, that contains both fixes: #1247
The current pull request can be disregarded.