Change requirements.txt file according to a fresh install.

According to pip-installer user_guild I change the requirements.txt file. For
each package there is a version. I just put all my installed packages from pip
freeze to requirements.txt.

For the moment the server is running with this requirements. When the time will
comes the version of some packages can be easy change.

pip guild: http://www.pip-installer.org/en/latest/user_guide.html