fixed blocking read transfer for the constant accessor: should only return on first read and then block forever

Forward declaration is taken from DeviceAccess header file, which solves problems if classes are moved to another namespace.

added missing cxx and linker flags from dependencies, removed some remaining traces of direct DOOCS dependency variables

also export the LIBRARY_DIRS variable to the calling CMakeLists.txt (needed to publish it to further downstream dependencies)

Fixed the confusing and inconsistently used names *_LINK_FLAGS and *_LINKER_FLAGS by always setting and getting both variables

Use mtca4u::setDMapFilePath() instead of the BackendFactory's member function. Since all applications will need it, the corresponding header file is now included in ApplicationCore.h

Removed the macros for defining accessors and introduced convenience classes instead. This adds slightly more syntactic sugar, but also allows more flexibility and seems to be a more coherent interface.

This commit incompatibly breaks the interface with the previous versions. Since ApplicationCore is not yet used in any productive environment, no compatibility is provided.

updated the example: use "using" syntax to inherit constructors and re-enabled the previously not working read-back of the device register "Variable".

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67054