Missing DownColorField from Candlestick docs

[marin-bratanov]

**Is there wrong information? **
Missing info

Is there a code snippet that does not work or throws errors?
No

Something else
The Candlestick article mentions the DownColor and ColorField, but does not mention the DownColorField and that ColorField values won't take priority over DownColor alone. See my comments at https://www.telerik.com/forums/colorfield-on-candlestick

[svdimitr]

Done with #699