[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
Treat message as CDATA to avoid invalid XML
Properly escape backtrace attributes to avoid invalid XML
Merge pull request #514 from mildavw/master

fix for notifier.js sending invalid XML
Merge pull request #517 from roryf/master

Fixes notifier.js sending invalid XML in backtrace lines
update changelog with new Pull request merge [ci-skip]
Pass problem when you UpdateProblemCache by rake task

Fix #518
update changelog with issue fix [ci-skip]
Sign in input set type=email for mobile browsers keyboard
Email only unless user_has_username
Merge pull request #519 from nyaa/email_input

Sign in: email input type=email for mobile browsers keyboard
Add documentation about all Env variable usage

Errbit can be config anly by ENV variable. We need a complete
documentation about it and improve this variable capabilities with not
only Heroku point of view
Improve information about ENV configuration
Fix spec because now the spec use TimeZone too in Mongoid
Add link to the ENV documentation from the README
Merge pull request #507 from shingara/features/improve_documentation_about_variable

[WIP] Features/improve documentation about env variable
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