fixed label disappearing bug for large axis values in graph3d

[gotoken]

Axis labels of graph3d is positioned on the middle point of between the origin and the center of each range. e.g.,

xText   = xRange.center() / 2;

For example, for xRange = [100, 200], the center of range is (100+200)/2 = 150 and the middle point is (0+150)/2 = 75 then the middle point is positioned out of range. So axis labels disappear. This patch uses points divide each range in the ratio 1:3 as axis label positions

I've setup preview https://fiddle.jshell.net/gotoken/5sk9ka72/3/show/ . Please try to reproduce by pasting this CSV into http://visjs.org/examples/graph3d/playground/index.html then click "Draw graph".

[mojoaxel]

@wimrijnders Can you please have a look at this.

[gotoken]

@mojoaxel Thanks you noticed him. I changed my patch to preserve original positioning way, that is, an axis label divides its range in the ratio 1:3. It may well be acceptable. Apologies for the changes after PR.

[wimrijnders]

@mojoaxel This fix is fine by me,

[mojoaxel]

approved by @wimrijnders