Stability and cleanup

• Added thumbnail_url to AdCreative object
• Added AutoComplete object
• Added get_by_ids() method e.g. AdSet.get_by_ids(ids=[123123,123123])
• Added the ability to define default account ID e.g. FacebookAdsApi.set_default_account_id('act_123123')
• Python 3 and 2.6 dict comprehension compatibility (thanks @agriffis!)
• Failing tests fixed
• Fixed bug with ABSOLUTE_OCPM not supplying API with allcaps (as speced)