fix issue that a double "-l" can appear in the Makefile config shell scripts for libraries which already contain the -l

Fixes DOOCS server shutdown lock-up

usage:
register_tests(SOURCES
                 ${list_of_source_files}
                 "test_src.cc"
                 ${concatenated_string_of_source_files}
               NAMESPACE
                 "test_namespace"
               LINK_LIBRARIES
                 ${list_of_targets}
               INCLUDE_DIRECTORIES
                 ${list_of_include_directories}
               COMPILE_OPTIONS
                 ${list_of_compile_options}
               WORKING_DIRECTORY
                 ${ctest_working_directory})

Introduced cmake module registerTests:

new scheme:
register_tests(SOURCES
                 ${list_of_source_files}
                 "test_src.cc"
                 ${concatenated_string_of_source_files}
               NAMESPACE
                 "test_namespace"
               LINK_LIBRARIES
                 ${list_of_targets}
               INCLUDE_DIRECTORIES
                 ${list_of_include_directories}
               COMPILE_OPTIONS
                 ${list_of_compile_options})

usage:
register_tests(SOURCES
                 ${list_of_source_files}
                 "test_src.cc"
                 ${concatenated_string_of_source_files}
               NAMESPACE
                 "test_namespace"
               DEPENDS
                 ${list_of_targets}
               INCLUDES
                 ${list_of_include_directories}
               COMPILE_OPTIONS
                 ${list_of_compile_options})

Function registers tests defined as a list of souce files.  Test defined
by file source_name.cc in the SOURCES list is registered under the name
  test_namespace.source_name

Provided list of dependent targets and include directories are used for
test executables as PRIVATE dependencies during compilation.

Function implicitly adds a dependency on the boost unit test framework
to each generated test executable.

This reverts commit 7eace484.

GNUInstallDirs doesn't really deliver the intended directories. CMAKE_INSTALL_LIBDIR e.g. points to lib/x86_64-linux-gnu on Ubuntu 16.04

Do not link against all boost libraries, since we must not link against the unit test library. The required libraries are already pulled in by the control system adapter anyway.

Not adding the repository as a remote simply makes it impossible to push
to it. Also this makes it mandatory to always fetch the changes from the
remote anyway since it is not locally mirrored.

Added persistency for D_spectrum properties. This resolves #11 partially only, since there is no option to switch it off. I am not sure if that is needed though.

Issue:
Server throws when there are no device module variables:

terminate called after throwing an instance of 'std::logic_error'
  what():  ReadAnyGroup has no element with AccessMode::wait_for_new_data.
Aborted (core dumped)

This commit introduces a workaround as proposed by jens:
  void DoocsUpdater::updateLoop(){
       if (_elementsToRead.empty()) {
           return;
       }

This commit is intended to be reverted if the above strategy has side
effects.