UE directory splits, creation of UE-specific files, common UE/eNB files and extraction of UE/common components from eNodeB files. renaming of files to minimize common names across directories (i.e. defs.h, vars.h, extern.h)

- fix compilation of dlsim/ulsim/oaisim by defining some needed
  global variables
- fix compilation of oaisim: compile coding and params_libconfig
- fix running of if4p5 with low CPU count (oaisim was not working
  on the machine 'haswell' because of this)

This work is based on work by NTT.

To use the code, do:
./build_oai --oaisim --ue-nas-use-tun -t ETHERNET -c

This commit only handles oaisim in S1 mode.

We won't handle noS1 mode.

Conflicts:
	cmake_targets/build_oai
	openair1/PHY/LTE_TRANSPORT/prach.c
	openair1/SCHED/phy_procedures_lte_ue.c
	targets/ARCH/COMMON/common_lib.h
	targets/RT/USER/lte-softmodem.c

Only ulsim and dlsim compile. The others (dlsim_tm4 pucchsim prachsim
pdcchsim pbchsim mbmssim) have been disabled.

Command line to compile: ./build_oai --phy_simulators

The following was not working properly:

    ./build_oai -I -w USRP

After this commit it works.

And so does:

  ./build_oai --eNB -w USRP

The following did not work before this commit
on ubuntu 17.10:

    ./build_oai --oaisim -c

oaisim has not been tested. It may fail to work. To be tested.