Unittest organization
In this PR I re-organize the unit-test folder and include few CMake files for that. Now the organization is as follows:
- unittest (root folder for c++ unit-tests)
- unittest/python (Python unit-tests folders, legacy from Python library)
- unittest/bindings (Python bindings for the moment)
@mnaveau be aware that you might need to code extra stuff inside unittest/CMakeLists.txt