Allow passing string hash values to AR order method

The order method from AR supports different kinds of arguments. When using a hash as the parameter, then this is supported:

```ruby
Topic.order(id: :desc)
```
but this is NOT:
```ruby
Topic.order(id: 'desc')
```

I think that is not what a developer would expect from a method like order, so I added a few changes to support that kind of capabilities. 

IMHO, this can be useful when passing 'ASC' or 'DESC' directly from the request params, like for a basic list sorting, without need of making conversions to symbols, which can be annoying or unclean in some situations...