Tags for configuring markers, and some fixes.

...0/app.core/src/main/java/tdt4140/gr1800/app/core/App.java

...e/src/main/java/tdt4140/gr1800/app/core/GeoLocations.java

...pp.core/src/main/java/tdt4140/gr1800/app/core/Tagged.java

...a/tdt4140/gr1800/app/doc/AbstractDocumentStorageImpl.java

...ain/java/tdt4140/gr1800/app/gpx/GpxDocumentConverter.java

...c/test/java/tdt4140/gr1800/app/core/GeoLocationsTest.java

...c/main/java/tdt4140/gr1800/app/ui/FileMenuController.java

.../src/main/java/tdt4140/gr1800/app/ui/FxAppController.java

...c/main/java/tdt4140/gr1800/app/ui/IMapMarkerProvider.java

...java/tdt4140/gr1800/app/ui/TagBasedMapMarkerProvider.java