Display select to choose http method in sandbox

In case you have a resource with several http methods (PUT|PATCH for example), you might want to choose the method to use. For now the first method is used by default (PUT|PATCH: PUT will be used).

The purpose of this PR is to allow to choose the HTTP method in case of several methods allowed via a select field, that's it.

![](http://i.imgur.com/d8GD83d.png)
![](http://i.imgur.com/EHPn7iJ.png)