Delete Garden Plan - first garden

#20 Deletion of first garden successfully implemented including confirmation prompt and flash notice.

Pending tests for multiple gardens.
This test should verify that the garden is no longer present.  As it is, it is only testing that the correct messages are shown.

I would structure this way:

~~~
Fabricate(:garden, user: @user, name: "The Best Garden")
visit '/'
page.should have_content("The Best Garden")
click_link "The Best Garden"
click_button "Delete This Garden"
click "Confirm Deletion"
page.should have_content("Your garden has been deleted.")
current_path.should == root_path
page.should_not have_content("The Best Garden")
~~~

You also need a scenario to cover if the user doesn't confirm the deletion.