Fix single image upload

src/main/java/NTNU/IDATT1002/controllers/DataExchange.java

src/main/java/NTNU/IDATT1002/models/GeoLocation.java

src/main/java/NTNU/IDATT1002/models/Histogram.java

src/main/java/NTNU/IDATT1002/models/Image.java

src/main/java/NTNU/IDATT1002/models/Metadata.java

src/main/java/NTNU/IDATT1002/service/ImageService.java

src/main/java/NTNU/IDATT1002/utils/MetaDataExtractor.java