[plugin] YouCompleteMe (YCM) config changes:

* Added autocmd config to handle C/C++ files and open global .ycm_extra_conf.py
* Disabled Vim preview window, because it affects YCM as well
* Added funtion to detect if a .ycm_extra_conf.py is present in the current dir
* YCM config reviewed and unnecessary options removed: sidebar error symbols,
  previe window, detail diagnosis

Change-Id: Ic47ec6d2b3aac0b25624ed940bda6ee8160ad229
[plugin] Replace spaces by  tabs in YCM global semantic completion files

Change-Id: I30f8787a432fcb46dc11209844eff1c86b0d6b3d
[plugin] Removed unnecessary code in YCM global semantic completion file

Change-Id: I84b0432c3202dcdcc4f8354ea015f8245ee0a8ea