New line injection during configuration edition

Cachet is an open source status page system. Prior to version 2.5.1, authenticated users, regardless of their privileges (User or Admin), can exploit a new line injection in the configuration edition feature (e.g. mail settings) and gain arbitrary code execution on the server. This issue was addressed in version 2.5.1 by improving `UpdateConfigCommandHandler` and preventing the use of new lines characters in new configuration values. As a workaround, only allow trusted source IP addresses to access to the administration dashboard.