Releasing 2.6.0-0

Signed-off-by: Ruben Smits <ruben.smits@intermodalics.eu>
cmake: add search for roscpp to support groovy, silently fails for fuerte

Signed-off-by: Ruben Smits <ruben.smits@intermodalics.eu>
new release: adds groovy support

Signed-off-by: Ruben Smits <ruben.smits@intermodalics.eu>