Add test for challenge index view
Use reverse for getting the absolute url
Add test for challenge display
Use class based view for challenge display
Fix: player could play a challenge without accepting it
Display error message when the challenge is Launched but not Accepted
Move the code for creating a challenge to setUp and test if error message is displayed when a challenge is not accepted
Use DetailView instead of View
Check if the challenge was refused
Added more tests
Use dispatch method to avoid code repetition
Test the view's POST method
Merge pull request #372 from badescunicu/refactorChallenge

Refactor challenge, use class based views and more tests.
Fix conflicts