Open the annotation bubble on click instead of hover

Showing / hiding the annotation bubble on hover causes many problems:

• It doesn't work on mobile
• you get the bubble when you move the mouse through the content even if you don't want to see the annotation bubble
• It's not obvious how to hide the bubble: the marker that triggers the bubble is outside the bubble. You need to move the mouse over the bubble and then out in order to close it.
• Writing functional tests is a PITA because the bubbles that show when Selenium moves the mouse hide the links or buttons that you want to click.