Group Fields in JSON column

[yanhao-li]

This PR is intended to provide a solution per discussion in #162.

A new trait HandleFieldsGroup was added, users have to create new json columns manually on the table, and for each column, the fields that needed to saved as group should be declared as $fieldsGroups in the repository, as the below example demonstrated.

class ProjectRepository extends ModuleRepository
{
    protected $fieldsGroups = [
        'fields_group' => [
            'field1',
            'field2',
            'field3'
        ]
    ];
}

Supported Fields:

• input
• wysiwyg
• date_picker
• select
• multi_select
• map (haven't tested, but should work)
• color
• checkbox
• checkboxes

Further improvements

• Support Browsers and Repeaters
• Added the fieldsGroups attribute to repository.stub
• Added it as a new option on ModuleMake CLI to add the json column automatically

Any comments/thoughts are welcomed!

[yanhao-li]

Because of the design of MultiSelected component, the stored json data for multi_select and checkboxes must be casted into the form in order to be displayed on the form

[
  ['id' => 'new york'],
  ['id' => 'london']
]

It's obviously not ideal, but may not in the scope of this PR, we should open another issue to improve the component.