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
some changes for the ValueRdfConverterTests
move test resources from src/main/resources to src/test/resources
Configured packaging properly

* Cleaned up assembly specifications for wdtk-distribution, using
dependencies instead of static, hard-to-maintain file paths
* Configure aggregate javadoc generation and use this in the
distribution (instead of copying unpacked files from many sources on top
of each other, overwriting existing files)

Preparing packages works with "mvn clean install -Psign" as before.
Merge branch 'master' of https://github.com/Wikidata/Wikidata-Toolkit.git
Fix maven configuration

The distribution module had dependencies that are only created in
profile "sign".
Merge branch 'master' of
https://github.com/Wikidata/Wikidata-Toolkit.git into
rdf-serializer_tests

Conflicts:
	wdtk-rdf/src/main/resources/GlobeCoordinatesValue.rdf
	wdtk-rdf/src/main/resources/QuantityValue.rdf
	wdtk-rdf/src/main/resources/TimeValue.rdf