feat(build): Added a new service leafletMarkerHelpers with the methods needed to manage the marker attribute
Moved the buldMarker function into the leafletMarkerHelpers service
Moved the deleteMarker function into the leafletMarkerHelpers service
Moved the createMarker function inside the leafletMarkerHelpers service
genDispatchEventCB made private
No need for the isDefinedAndNotNull function anymore
Small change on chekers
feat(build): We can disable the watch on the markers adding a 'watch-markers="no"' to our directive. Thanks to @fwitzke.

Changed the way to configure it. Now we must use:
<leaflet markers="markers" watch-markers="no"></leaflet>

ISSUE: https://github.com/tombatossals/angular-leaflet-directive/pull/210