title: mixin vs plugin. What to choose?
body: <p>Let's assume I have defined several new components -<code>MyComponent1</code>, <code>MyComponent2</code>, ..., which extend <code>Ext.Component</code>.</p>
  
  <p>Now I wnat to extend all this widgets with the same functionality - I want to add <code>close</code> button which would appear at the top-right position of <code>MyComponentX.el</code>.</p>
  
  <p>What should I use: <code>mixin</code>? <code>plugin</code>? or something else?<br>
  And in general: <code>mixin vs plugin</code>, what is the best practise?</p>