Map Geo Location - Frontend - marker placement

[dclermont90]

• currently the map marker are placed on the wrong districts
• also the marker of the sub districts are gathered at the center of the map if a district is selected
• don't display any marker if there is no geo data available for a specific marker

[krausweb]

Done during to https://github.com/nextsolx/ratsinformationssystem/pull/65