Moved test & onelogin requirements to the setup.py extras_require section.

[scriptsrc]

Moved the python-saml lib to an extras section.
Also, moved testing libs to their own extras section.

Now, libxmlsec1-dev is no longer required.

.travis.yml modified to install the tests requirements:

• pip install .[tests]

If you'd like to use onelogin, you simply need to run these commands:

• sudo apt-get -qq update
• sudo apt-get install -y libxml2-dev libxmlsec1-dev
• pip install .[onelogin]

    extras_require = {
        'onelogin': ['python-saml>=2.2.0'],
        'tests': [
            'nose==1.3.0',
            'mock==1.0.1',
            'moto==0.4.25',
            'freezegun>=0.3.7'
        ]
    }