Enable textarea to be defined in schema

This will enable the following example to work:

1. **client/config.js**
```javascript
SimpleSchema.extendOptions({
  rows: Match.Optional( Number ),
});
```

2. **client/schemas.js**
```javascript
Schemas = {};
Schemas.myAwesomeSchema = new SimpleSchema({
  notes: {
    type: String,
    label: "Notes",
    rows: 3,
    optional: true,
    max: 1000
  }
});
```

3. **client/views/form.html**
```javascript
<template name="form">
  {{>quickForm schema=myAwesomeSchema}}
</template>
```

**Result**
A quickForm where 'notes' is rendered as a textarea, without having to use afQuickField