Fix #446 -- Choices for Event.currenxy attribute (#452)

* Change event currency to a choice attribute

* Added pycountry to requirements for currency list

* Fixed issues from flake8

* Added tests for event currency and added pycountry to setup.py

* Removed whitespace from test/control/test_events.py

src/setup.py

@@ -98,7 +98,8 @@ setup(
         'chardet>=2.3,<3',
         'mt-940==3.2',
         'django-i18nfield',
-        'vobject==0.9.*'
+        'vobject==0.9.*',
+        'pycountry'
     ],
     extras_require={
         'dev': [