Leaflet widget

[rveciana]

This PR adds the possibility to select a point in a map and get its coordinates.
The following options are available:

• height: Heigh of the map element. 200px by default
• zoom: The initial map zoom level. 13 by default
• useUserPosition: If true, the map takes the location from the browser and will center the point there as the initial position
• initialLatitude: The initial latitude to show the map and marker
• initilaLongitude: The initial Longitude to show the map and marker
• tileAddress: By default, OpenStreetMap, but any can be used
• tileAttribution: The attribution to show on the map (mandatory on OpenStreetMap)