Defines a module function that can perform a click action on an element. The function name is derived by action_name.

When scoped to a collection it requires an element be passed to the action.

## Example

  # without a collection
  defmodule MyPage do
    use PageObject

    clickable :submit, "form button"
  end

  # click form submit button
  MyPage.submit

  # with a collection
  defmodule MyPage do
    use PageObject

    collection :things, ".thing" do
      clickable :submit, "button"
    end
  end

  # click button of 0th item in things
  |> MyPage.Things.get(0)
  MyPage.Things.submit