Line chart: increase number of x axis breaks when dates are a range

[c-buchan]

When time periods for an indicator are a range* (e.g. 2012-13), only the first and last time periods are shown on the x axis - e.g. domestic electricity consumption

It would be good if there could be intermediate periods plotted.

*except not all indicators with ranges, as doesn't seem to be the case for children in relative poverty

[Shiny-Penny]

Request from the closed ticket:

In the line chart within the indicator pages, for some indicators it only shows the first and last year of the time series. They should be shown at every few intervals on the axis. Indicators impacted are electric vehicle charging devices, further education achievements, apprenticeship starts and achievements for both Eng and Scot, electricity consumption and gas consumption.