title: How to have ToggleButtons stop being pressed "down" only when another toggle is Pressed
body: <p>I have a set of Python Kivy ToggleButtons which are all apart of the same group, e.g.</p>
  <pre><code>self.add_widget(CustomToggleButton(&quot;0&quot;, &quot;group1&quot;))
  self.add_widget(CustomToggleButton(&quot;1&quot;, &quot;group1&quot;))
  self.add_widget(CustomToggleButton(&quot;2&quot;, &quot;group1&quot;))
  self.add_widget(CustomToggleButton(&quot;3&quot;, &quot;group1&quot;))
  self.add_widget(CustomToggleButton(&quot;4&quot;, &quot;group1&quot;))
  self.add_widget(CustomToggleButton(&quot;5&quot;, &quot;group1&quot;))
  
  </code></pre>
  <p>Because they are part of the same group only one can be pressed at a time. This is the desired behavior, however I want to also disable the ability to &quot;re-click&quot; on a pressed down toggle button to turn it off. i.e. the user will only be able to turn the toggle button off by turning another one on.</p>