Deploy update site to Maven Central

[reckart]

Describe the refactoring action
All UIMA JARs that should be needed by the Eclipse plugins including the Eclipse plugin bundles themselves should be deployed to Maven Central. If that is the case, it should be able to deploy a p2 update site to Maven Central as well. We already have some babysteps towards this in the uimaj-eclipse-maven-p2-site but it is not production-ready yet.

The old update-site building process can then be removed and the old update site at ASF eventually be archived.

Expected benefit
Streamline release process.