If a row object's `content` is empty, the selection is the entire row object instead.

Note the row object may have been transformed by ember-timetree, so it is not identical to the user's original input.
don't append "undefined" className to sections
apply .hover and .selected classes to hierarchy labels too
scrubber text should have a little margin with the x-axis
Show durations on sections too.

* Only highlight a bar section when it is hovered, not when the whole duration is.
* Mark sectional bars with .sectional.
* Group rect and duration text elements for reuse.
remove magic -6 so brush is flush with its axis
Scrubber timestamp stays in sync with brush view.
README.md and basic CSS to get you started.
pre-built version of ember-timetree for the current tag