Enhance compilation of markers and labels

In pull request #526, I added a simple way to compile angular templates in makers. But this solution was not enough, especially if the template used the ng-include directive. The asynchronous loading of template left the popup improperly sized for it's compiled content.

Because this compilation needs to take place each time a popup is opened, I refactored the implementation of opening popups.

In addition, the same compile operation is applied to labels if the leaflet.label plugin is used, rendering the template in labels also.

Examples are added to both marker popups and labels.