Improved import_from_geoserver script

Related to Isuue #1
- now datasets are being added to group cambodia
- implemented upload for GeoJson resource (still not working as wished)
Modified plugin.py to store taxonomy as tags

Realted to Issue #3 „ Reproducing ODC's taxonomy with Tag vocabularies „
Implemented File Upload for GEOJson files

Related to Issue #1

Now GEOJson files are being uploaded in the import script in order to
avoid resource too big problems.