Improve Date to be allow to use for Date From and Date To

[nasrulhazim]

This PR enabled developers to have a nice Date From and Date To Feature - Date Range.

To enable developers to use the feature simply create new Filter, then extend the R64\Filters\DateFilter class, then define as following:

The Setup

namespace App\Nova\Filters;

class DateFrom extends Date
{
    public $date_field = 'created_at';

    public $is_date_from = true;
}

namespace App\Nova\Filters;

class DateTo extends Date
{
    public $date_field = 'created_at';

    public $is_date_to = true;
}

The Usage

...
    public function filters(Request $request)
    {
        return [
            new Filters\DateFrom(),
            new Filters\DateTo(),
        ];
    }
...

Others

Other than this feature, developers may define public $options to define Date config

[nasrulhazim]

if you don't define $is_date_from or $is_date_to, the operand will be use is =.

public $date_field is mandatory since we need to which column to be use for checking.

[beliolfa]

Thanks for your PR!
I think that it fits better if getDateField were an abstract method. But in the other hand I dont want to force the user to declare it if they want to use the DateFilter as usual (declaring their own apply). I dont know why but I see this feature a bit breaking.
Let me think about it :)