Add read abilities for Challenge
More abilities for challenge
Use cancan to authorize controller
Adding challenges users model
Merge pull request #65 from ijustwanttocode/jr/challenges_part2

[challenges] Add cancan for Challenge
Merge branch 'development' into jr/challenge_participants
Merge pull request #68 from ijustwanttocode/jr/challenge_participants

[challenges] Add challenge participants
Merging in dev; fixing Gemfile conflicts
Adding specs and some cleanup