ModuleList serves as a container for VariableGroups. The VariableGroups
mirror xml modules in the config file.

Xml parsing logic factored out to class ConfigParser.

- Make doxygen pick up markdown.
- introduced: set_default_build_to_release.cmake

set_default_build_type_to_release.cmake -> set_default_build_to_release.cmake

- add test for full exception handling

  DeviceModule and ControlSystemModule now do not take the optional prefix argument in their constructors any more. Use the [] operator instead to get the submodule.

- Add ExceptionHandlingDecorator and decorate all device variables with it.

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

'*.md' files put into the projects doc directory will be picked as part of
the documentation. '*.md' files in other locations of the source tree will
be ignored.

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.