[WIP] Start refactoring the problems_controller.

1) Limit some before_filter using the expose system
2) Extract some view test in view spec instead of controller spec
[WIP] refactor the problems_controller

Extract the filter `find_problem` in decent_exposure to get this problem
Merge branch 'master' into refactor/problem_controller
Little refactoring of action in ProblemController
Move the spec fabricator in model spec. It's more related
Refactor ProblemController

Extract some instance variable in DecentExposure
extract same usage of params in ProblemController and AppController
Refactoring of AppsController

 * Stop using inherited_resources and only decent_exposure
 * Use decent_exposure when it's possible
 * Extract some translation
Merge pull request #521 from shingara/refactor/problem_controller

Refactor/problem controller