Fixes DOOCS server shutdown lock-up

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.

- update dependency versions

- Replace the std::reference_wrapper<TransferElement> with a TransferElementAbstractor.

Fixed a type confusion between int64_t (aka long int on 64 bit platforms) and long long int. The types are not identical (in the C++ sense) but bit-compatible. ChimeraTK expects int64_t while DOOCS expects long long int.

add enable_latest_cxx_support.cmake and added a comment to enable_cxx11_support.cmake to no longer use is.