Add requests as a requirement

Unclear why this was commented-out previously, this exception occurs when requests is not first installed:

```
Obtaining ec-paypal from git+git@github.com:5monkeys/ec-paypal.git#egg=ec_paypal (from -r requirements/base.txt (line 31))
  Cloning git@github.com:5monkeys/ec-paypal.git to ./env/src/ec-paypal
  Running setup.py egg_info for package ec-paypal
    Traceback (most recent call last):
      File "<string>", line 16, in <module>
      File "/Volumes/fem-viskande-apor/theclan/env/src/ec-paypal/setup.py", line 8, in <module>
        version=__import__(name).__version__,
      File "ec_paypal/__init__.py", line 1, in <module>
        from .api import *
      File "ec_paypal/api.py", line 1, in <module>
        import requests
    ImportError: No module named requests
```