Validate all input params

Respond with a `422` to any request that includes bad parameters.

Refactors the way validation of parameters is done to use a `ValidInputFilter` which is given validators when wiring it up in the application.

[Trello ticket](https://trello.com/c/3WanMsv4/347-422-all-the-email-alert-api-endpoints-if-params-are-bad-2)