It can be static and it may make sense to use it outside modules. The implementation should probably move to a Application member function to make it easier to reach from non-module code.

This is to support when running under Boost::Test which will swallow the
message otherwise and print the confusing ~AppBase() message of not
being properly shut down

move ApplicationModule::appConfig() to ModuleImpl::appConfig() so it can also be used from ModuleGroup

fixed connectTo() so it now uses the dynamic/virtual model and thus obeys e.g. eliminated hierarchies etc.