title: lit element property passing too another function/class
body: <p>I am currently learning how to use lit-elements, and i am also faily new with web development. I am trying to make a bluetooth custom element that changes a buton text and color depending on if the bluetooth device is connected or not. </p>
  
  <p>In my litelement I create another class called BTLE, where all the bluetooth is handled.
  But I have no idea how to pass a litelement property to this BTLE class.
  I want my button to get re-rendered when the BTLE class notices a connect or disconnet. 
  If I pass a property through the BTLE class via the constuctor and I change the property the button is not re-rendered. If I change the propery inside the litelement class it gets re-rendered.</p>