* extends mailer class with bcc based mailing
* switches all team based mail sending (multiple mail adresses) to bcc based mailing
* adds smaller versions of tech-croc error images for 4xx and 5xx errors for faster rendering
* adds proper handling in case of BadRequest (error 400)
* enhances html template for error 500
* adds new html template for error 400
* adds uuid_required decorator to missing views
* updates translations
