4291: Clean up HTTP methods in Workbench URL generators.

4291: Clean up HTTP methods in Workbench URL generators.

According to the docs at
<http://api.rubyonrails.org/files/actionview/lib/action_view/helpers/url_helper_rb.html>:

* `button_to` and `form_for` take :method as a symbol.
* `link_to` takes :method as a symbol, and only supports :delete,
  :post, :patch, and :put.  Any link that should be done with GET
  should not have a method specified.
* Note that `form_tag` *does* take a string, so not every method
  should be symbolized.