Tick stroke and tick text stroke properties in charts

[arisgk]

I could not change the tick stroke and tick text stroke using properties. Adding them as props in chart components did the trick. I added tickTextStroke into axis components propTypes too. It is my very first open source contribution so tell me if I did anything wrong in the process.

[yang-wei]

oh @arisgk thanks for this but instead of adding each propTypes to each chart, I prefer you to add them to CartesianChartPropsMixin.js

You can take a look how this is done in another pr - #27

And also welcome to OSS

[arisgk]

Okay, @yang-wei do you think it is better to go for separate xAxisTickStroke and yAxisTickStroke or a common tickStroke prop for both axes?

[yang-wei]

separate will be fine since this is how our API looks like

[arisgk]

@yang-wei I added xAxisTickStroke, xAxisTickTextStroke, yAxisTickStroke, yAxisTickTextStroke to CartesianChartPropsMixin.js.

[yang-wei]

will merge in #70