Fixed issue #51 (Maven package signing)

The correct command to create signed packages is:
* mvn clean install -Psign
or (if you don't care about typing your passphrase into a command line):
* mvn clean install -Psign -Dgpg.passphrase=x
move test resources from src/main/resources to src/test/resources
Merge branch 'master' of https://github.com/Wikidata/Wikidata-Toolkit into create-parser-of-constraints