updated the Elk interface to fix some minor bugs which arose for certain systems with equivalent atoms. I've also included new tests for this interface and collated all of these interface tests in the "test/python/elk" subdirectory.
* moved the plovasp C++ code to c++/triqs_dft_tools/converters/vasp
* added global header triqs_dft_tools/triqs_dft_tools.hpp
* python dir based on single cmakelist file
* registered C++ tests for plovasp
* corrected imports for py3 tests for plovasp
* corrected block order in sigma_from_file and srvo3_Gloc
* exchanged ref files for sigma_from_file, srvo3_Gloc, SrVO3.ref.h5
* moved vasp converter bash scripts from dir shells to bin dir
The main change is that `test_all.py` is now renamed to `run_suite.py`,
with the latter being able to run a selected test suite if a corresponding
command line argument (test suite directory name) is provided.
CMakeLists are improved to copy each test suite separately to avoid
copying unnecessary files. Also each test suite corresponds now to
a separate CMake test.
