Simplify the API calls for charts

[prykon]

I think there's room for improving the starter code for the charts/one-page-chart-template.js page.

Room for improvement:

• The current example snippet for loading a chart has hardcoded data (reference here)

• Instead of having the button that calls the sample API and having the API response change that button's text, I propose we add an API call that gets executed on page load instead of on click and that the response update the chart's data.

• If an example of the chart data array structure is desired, instead of deleting the hardcoded values we could add a commented example or a link to amchart's documentation for that graphic type.

Reasons for the change:

• There is no reasonable scenario for having hardcoded chart data
• Having a snippet that loads the chart's data by API on page load is a much more relevant feature (probably even the most important one) for what users will want to achieve with this page.