report the actual url as request_url

Reporting the hash turns (for me) out to be error prone as I do not get the actual host.
move the validations for error_class and environment from Err to Problem

Problems are the models rendered in the UI now, not Errs. Errs are functioning as a glorified hash table. It makes more sense to validate problems.

Also, this paves the way for the next commit, so that no functionality is lost in the subsequent refactor.
Errs are like a hash table whose values are arrays of notices and whose keys are a composite of error_class + component + action + environment + backtrace[0..3].

These fields no longer need to be cached separately on Err because they are now cached on Problem.

This commit combines all those values into one simple key: fingerprint. This should:

 - Make err lookups faster
 - Make it easier to reason about, test, and replace the fingerprint algorithm
 - Make the relationship between Problems, Errs, and Notices clearer
[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
Added jira as new issue tracker
Fix spelling in README [ci skip]
Merge pull request #520 from crymer11/patch-1

Fix spelling in README [ci skip]
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
Avoid setting MongoDB all the time

We can have no env variable. So we don't need configure Mongoid

see #461
Refactoring of AppsController

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

Refactor/problem controller
Move some test view in spec/views instead of render_views in
spec/controllers
Move the spec about apps/show.atom.builder in his own spec
Avoid require issue_tracker model directly in Gemfile when it's not
needed
Update javascript-stacktrace to tag 0.5.3.