More eligibility and group updates (#506) (#507)

* Improve challenge visibility control (#501)

* IMPROVE CHALLENGE VISIBILITY CONTROL
(https://www.topcoder.com/challenge-details/30057891/?type=develop)

Verification guide: docs/Verification_Guide-Improve Challenge Visibility Control.doc

* Restoring an accidentially modified file

* Fixed the case with a challenge that doesn't have eligibility

* Shared the eligibility verification with challengeRegistration.
The eligibility check routine is now in challengeHelper and can be added anywhere by a couple of simple lines of code.

* improve the query

* update query for groups (#502)

* Update queries (#503)

improve logging for v3 api call

* should use externalToken field name

* update queries for group checking

* Improve challenge visibility control: getChallenge and getRegistrants (#504)

* IMPROVE CHALLENGE VISIBILITY CONTROL
(https://www.topcoder.com/challenge-details/30057891/?type=develop)

Verification guide: docs/Verification_Guide-Improve Challenge Visibility Control.doc

* Restoring an accidentially modified file

* Fixed the case with a challenge that doesn't have eligibility

* Shared the eligibility verification with challengeRegistration.
The eligibility check routine is now in challengeHelper and can be added anywhere by a couple of simple lines of code.

* Improve challenge visibility control: getChallenge and getRegistrants

* revert commit

Author: skyhit