Data table hover and selection improvements

[nrenner]

#241 follow-up

Adds:

• switch to turn off hover synchronization with map
• data row selectable by click (based on Row selection example)
  keeps selection and map highlight until clicked again, centers on map, disables hover sync
• use Polyline.getCenter() instead of bounds
  Returns point on line at half distance instead of centroid of bounds,
  which can be far off the line for curved lines and not show line at high
  zooms.