Added dynamic languages via command

- Use -nominatim-import-languages command with comma separated
languages to load those languages during import
- Use -nominatim-import-languages command with comma seperated
languages to use certain languages during run

Example: -nominatim-import-languages en,de,nl
Fix invalid json
Seperated language commands for import/running

Use -nominatim-import-languages for importing and -supported-languages
for runtime languages
Added dutch (nl) to mappings.json
Added stripNonDigits util
Fixed ImporterTest to use (static) languages
Added postcode check for nl postcodes

- Filter doubles out if there are highways with the same name &
postcode numbers when language is 'nl' (i.e. the same street has 6532RA
and 6532BE, which should only be returned once to prevent clutter in
autocomplete)
Fixed tests to use new lang scheme
Added Netbeans xml to .gitignore