DB Filter Flexbility

[patrickheeney]

Right now you can only add filters for columns with relations. We should expand this to include all kinds of filters. The "switchers" should be removed in favor of a boolean type filter. We should add other types to search by integers (for example a filter to show products <$XXX) and searching on text fields. Also need to include the appropriate views:

Maybe the Db_FilterBehavior can have a formRender to create complex type filters using $custom_columns. Something like:

class Shop_ProductFilter extends Db_DbFilter
{
    function define_columns()
    {
        $this->define_column('price')->renderAs(frm_text);
    }

    function define_form_fields()
    {
        $this->add_form_field('price', 'left')
    }
}