Reorganization of the test directory

- Moved the contents of the test/ directory to test/oglplus/.
Minor change in the build system.

- Moved the oglplus-advanced-examples target to parent CMakeLists file.
Minor changes in ops/application

- Removed dependencies on String and config.hpp
Multiple changes

- Added #undef MemoryBarrier to context/synchronization.
- Added explanatory notes, why it is necessary.
Merge branch 'develop' into feature-oalplus
Minor updates in the Spectra advanced example
Merge branch 'develop' into feature-oalplus