Add Chart Axis Label modifiers

[murtza]

Closes #34
Closes #35
Closes #36
Closes #37

Screenshot

<Chart modifiers={
      @native
      |> chart_x_axis_label(title: "ABC")
      |> chart_y_axis_label(title: "XYZ")
    }>
...
</Chart>

[carson-katri]

Looks like this is using some types from #89, so we could wait until that is merged.