This reverts commit 5f8a6122.

- Add missing build/ folder.
- Add .gitignore.
- Fix cmake Find modules.

In ALL (trunk):
- Improvements on the previous cmake commits.

In Elementary_utils (trunk):
- Add the installation routines in CMakeLists.
- Add doxyfile.

In NumA++ (trunk):
- Add the installation routines in CMakeLists.
- Add FindElementaryUtils.cmake module and adapt CMakeLists.

In NumA++_Tests (trunk):
- Add FindElementaryUtils.cmake & FindNumA++.cmake modules and adapt CMakeLists.

In PARTONS (trunk):
- Add the installation routines in CMakeLists.
- Add FindElementaryUtils.cmake & FindNumA++.cmake modules and adapt CMakeLists.

In PARTONS_exe, PARTONS_release, PARTONS_Tests, PARTONS_Fits (trunk):
- Add FindElementaryUtils.cmake, FindNumA++.cmake & FindPARTONS.cmake modules and adapt CMakeLists.