Clickable Legend Titles

[alexshoe]

Description:

Adds the ability to click/double-click on legend titles to toggle legend visibility, making it easier to manage complex charts with multiple legends.

Example:

layout: {
  legend: {
    title: { text: 'My Legend' },
    titleclick: 'toggle',  // toggles the legend to which the clicked title belongs
    titledoubleclick: 'toggleothers' // toggles on/off all other legends
  }
}