Added :resource to attr_accessible in FlowTaskResource

To allow for assignments such as these:
```ruby
    ft = FlowTask.new
    ft.inputs.build(:resource => some_object)
```

In addition to:

```ruby
    ft = FlowTask.new
    ft.inputs.build(:resource_id => some_object.id, :resource.type => some_object.class.to_s)
```