Removing "incubator" package name (incompatible API change)

[svanteschubert]

This I would call a mistake from the past. Once meant as a "beta" tag, could have been solved easier with a "Beta" Java annotation like Guava is doing.

For, the 1.0 release these "incubator" packages will be removed as incompatible API change - requiring a search/replace from existing users.