Fix issue with missing parent_id and setting default parent id to null

Summary:
Missing parent_id attribute was causing tests to fail.
Resetting default parent id to None was also causing it to fail

Test Plan: run tests, profit
ABSOLUTE_OCPM changed to  upper case as required by our api

Summary: BidType constant was lower-case and that impeded to create a local awareness adset on an example i'm creating

Test Plan:
execute the local_awareness.py file putting your adaccount in the 'env' variable. it should fail. apply this patch and it should work.

content of the script: https://phabricator.fb.com/P18123548
Added autocomplete endpoint

Summary: Allow users to access the autocomplete endpoint using the SDK.

Test Plan:
You can do this in the REPL
```
ac = AutoComplete(parent_id='act_11124366')
print ac.remote_read({
    'q': 'United States',
    'type': AutoComplete.Type.adcountry,
})
```
params['fields'] not defined properly when fields parameter not provided

Summary:
Refactored some fields handling code and introduced a bug that would sometimes
result in params['fields'] to be completely undefined.

Test Plan: run tests
Tox for testing on Pythons 2.6, 2.7, 3.3, 3.4
Automated testing w/ Travis CI.
Point Travis badge at agriffis/facebook-python-ads-sdk?branch=all