The user can now also choose to publish messages only to the control
system.

Refactored.

Reading was done only in deeper levels inside the VariableGroups.

See 1af92147. Input accessors are now properly part of the ReadAny group which improves the deterministic behaviour.

This provides a strict guarantee for the order of updates w.r.t. trigger, especially for tests.

  - Removed extra call to registerModule which caused multiple creation
    of the same module on a tree node
  - Made addChildNode private

Instead of holding the modules in a flat list as before, this represents
the ownership of nested modules correctly and prevents possible memory
access violation on destruction.

Currently does not get the modules in a way that they can be downcasted
to test if StatusMonitor, etc

Correctly navigate to parent module via virtual path.

If someone includes the Logger into an ApplcationModule and calls writeAll() the Logger variable message will be written. To catch that cases set message empty after calling sendMessage and ignore empty messages in the LoggingModule.

    - Basic structure of test application
    - Added modules
    - Refactoring of StatusMonitor to provide a non-templated base class
    - Needs follow-up, for status see issue #14 and the linked follow-up
      ticket

- ConfigReader is in ApplicationCore.h, but was including ApplicationCore.h itself
- Added include guards to ApplicationCore.h, although it's not stricktly needed (all included headers have one). Might speed up complilation because it makes it easier for the parser.