don't concatenate validation error responses, only use first one.
fixed bug where concatenating validation responses by default

added tests and fixes for `join_responses` validation option

Warning: breaking change here with settings schema. Error responses
message will not be joined by default now, only the first validation
error response is sent unless the `join_responses` setting is true.

Validations settings schema now includes join_responses, so if you
upgrade to this version you will need to migrate your settings to the
new schema.

JSON app_settings have changed from:

```
validations: [
    {
        property: 'patient_name',
        rule: 'lenMin(5)',
        message: 'please include patient name'
    },
    ...
]
```

to:

```
validations: {
    join_responses: <bool>,
    list: [
        {
            property: 'patient_name',
            rule: 'lenMin(5)',
            message: 'please include patient name'
        },
        ...
    ]
}
```