Improve test Boostrap controll + Allow skipping integration tests for gated features + Improve config inline docs

Summary: Improve test Boostrap controll + Allow skipping integration tests for gated features + Improve config inline docs

Test Plan: update your config.php than run tests
Fix wrong FQN reference to \Facebook\HttpClients\FacebookCurl

Summary: Fix wrong FQN reference to \Facebook\HttpClients\FacebookCurl

Test Plan: instanciate a new \FacebookAds\HttpClient supplying a FacebookCurl object
Fixed getReachEstimate in the PHP Ads API SDK.

Summary: Previously the SDK was returning a cursor object. I've normalized the return type between AdAccount and AdGroup's getReachEstimate() calls to return a ReachEstimate object instead of a cursor. I've also defined the ReachEstimate fields as constants.

Test Plan: Automated fetch tests in AdGroup and AdAccount. Observe results when running https://phabricator.fb.com/P16861941 for populated fields in the var_dump.
Implement native http layer + remove php-v4 as dependency + reorganize dir structure

Summary: remove php-v4 as dependency

Test Plan: run tests
Update README.md + examples to v2.2.0

Summary: Update README.md + examples to v2.2.0

Test Plan: Read + try examples
Fix AdVideo::create() + use dedicated domain graph-video

Summary: Fix AdVideo::create()

Test Plan: run tests
Comply with v2.2 changes + update tests

Summary: Comply with v2.2 changes

Test Plan: run tests
Update DEVELOPER_GUIDE.md + Decontextualize bid types

Summary: Update DEVELOPER_GUIDE.md + Decontextualize bid types

Test Plan: read + run tests