Tip component (and popover component)

The tip component is a simple container for an inline label and a bit of help text to go along with it in the form of a tooltip.

The popover component is a general purpose pane that is associated with an anchor element. It is the tooltip for the tip component, but it can do more than it. Notably, it encapsulates all the top left fiddling that needs to be done to keep the pane on the screen and the arrow always pointing at the anchor.
I'm too lazy to test to see what happens if there's no `.arrow` element; is all of the arrow related stuff a no-op if it is omitted from the template?