Create Challenge : Validate Group Ids are valid or not

[sarojbehera1]

No description provided.

[liuliquan]

1. There is an existing helper.getGroupById function, should use that function to get group by id
2. The validation logic for groups existence are almost same for create/update challenge, should create a new common function to validate.
3. Use Promise.all() to retrieve groups in parallel, something like https://github.com/topcoder-platform/challenge-api/blob/dev/src/services/ChallengeService.js#L490-L501