Start/stop bundles in parallel for better performance

Since most computers have multicore processors by now, it would make sense to start/stop all bundles with the same start level in parallel. This has the potential to greatly decrease the startup/shutdown time and would be a good investment into the future since it's likely that the number of cores will increase further.

In our environment, 69% of all bundles have the default start level of 20. The next 19% of the bundles share 4 different start levels.

Before this change is implemented, it has to be checked if it is compatible with the OSGi specification.