Check that citydata exists for aggregation before displaying
Allow ordering of indicators by value
Allow paginate Indicators by page_size param
Add legend for indicator map page

Update oti-legend directive with style param, allows
    either 'flat' or 'stacked' style

Dynamically create legend max/min values from indicator values

Add OTIMapStyleService:
    Has stubs for future functionality, like custom legends
    per indicator type

TODO: Send CartoCSS style for each indicator to windshaft from angular
      BLOCKED on scala geom fix
Merge pull request #311 from WorldBank-Transport/feature/indicator-legend

Feature/indicator legend