Merge remote-tracking branch 'origin/develop_integration_2018_w19' into develop

Summary of changes:
- split UE and eNB directories
- nFAPI L2 emulator
- basic simulator
- various bug fixes

The nFAPI L2 emulator is not functional yet. Some code had to be removed
because it made the monolithic eNB non functional.

The unitary simulators (ulsim, dlsim) do not compile anymore. This will
be fixed later.