Shareabouts.js 3.6.3

Update to better support "standard" GeoJSON features

• Treat icons and vectors different consistently

  Before, if we had, say style and focusLayer properties on a style rule,
  the map would get confused because it would try to setIcon on a layer that
  doesn't have such a function. This release updates the focusLayer and
  unfocusLayer methods to be smarter about this.

• Add a SimpleStyle attribute to the Shareabouts.Utils for properties and
  methods that have to do with simple styles.

• Update the getStyleRule method to take simple styles into account.