Update target definitions to eclipse 2018-12 - Update nightly target to 2018-12 - Update release target to 2018-12 - Remove oxygen target - Create previous-release target (2018-09) - Update maven configuration - Remove EMF Compare from p2 repository Change-Id: Iecd0f3bd7b40ebe80637048431afa60461eec209 Signed-off-by: Tobias Ortmayr <tortmayr@eclipsesource.com>