Fix clone method

Closes #135
Added Http Status 303 to allowed redirect Types
Merge pull request #153 from papoms/master

Follow Redirects with HTTP Status Code 303
Merge pull request #142 from fzaninotto/fix_proxy

Fix clone method
Add mention of webhooks plugin in README
Prevent the creatino of empty checks

Closes #151
Merge pull request #154 from fzaninotto/prevent_empty_check

Prevent the creation of empty checks
Add pattern detection in response body

Closes #143, #150
Merge pull request #155 from fzaninotto/pattern_detection

Add pattern detection in response body
Add mention of the campfire plugin
Replace memory store by cookie store to avoid warnings in production

Closes #115
Merge pull request #156 from fzaninotto/session_cookie

Replace memory store by cookie store to avoid warnings in production
Update Changelog
Add second screenshot
Reduce screenshots to take less vertical space
Fix typo in current version
Prevent app from crashing when passed an incorrect Regexp

Closes #157
Refactor pollers to allow better extensibility
Allow the setting of custom poll types in the check edit form
Make pollers more robust to avoid fatal errors