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

add ConfigReader.h to ApplicationCore.h, as the ConfigReader is now more strongly integrated with ApplicationCore

add test for findTag() (was never really tested before), including advanced features like HierarchyModifier::moveToRoot

Implemented first part of #17: A HierarchyModifier can now be specified instead of the eliminateHierarchy boolean flag. No new functionality is yet added.

Exception handling

- reformatted source code

- added more comments
- need to catch exception by reference, else the message seems to be lost
- test if the message is correct
- test if device is really closed and opened again
- changed names of status variables in control system to match the general naming conventions