Moving ownership to DISCOTools project

[kengu]

I've sent a request for maven repository hosting to Sonatype, which is now granted.

Issue #4 updated maven groupid and java/gwt namespace to org.discotools.gwt.leaflet.
Next step is to move ownership of gwt-leaflet to DISCOTools.

I will use "the github way", following this procedure.

Note: Any followers that want to track the new remote instead of this soon-to-be personal clone,
have to run the following command locally:

git remote set-url origin https://github.com/DISCOTools/gwt-leaflet.git

Reference

Changing a remote's URL