Scott Bedard f628eaf666 Adds "required" component properties
Adds a "required" and "requiredMessage" key to component properties. If a required field does not have a requiredMessage, a default message of "Required fields were left blank." will be used.

Example usage...
```php
public function defineProperties()
{
    return [
        'maxItems' => [
             'title'             => 'Max items',
             'description'       => 'The most amount of todo items allowed',
             'type'              => 'string',
             'required'          => true,
             'requiredMessage'   => 'You must set the maximum todo items allowed!'
        ]
    ];
}
```
2015-01-09 19:12:21 -05:00
..
2014-05-14 23:24:20 +10:00
2014-12-01 12:20:04 +01:00
2015-01-09 19:12:21 -05:00