title: Libgdx Box2D controll collision response for a few specific objects only
body: <p>In <code>Box2d</code>, as much as i understood, objects have a default collision response, which lets them stop movement or bounce back (if you set a restitution).<br>
  Also you can say, that the object is a sensor and so you can implement your own collision response.<br>
  Now i would like to use the default collision response for some kinds of collisions, while i want to have full controll of collisions with specific objects.<br>
  For example: A player should stop movement or bounce back, if he collides with a wall, but it should loose Hp, when he collides with a bullet and the bullet should be removed.<br>
  So i would like to have something like the contact filters, but the objects, which do not match the filter should react with the default behaivor.  </p>
  
  <p>Is something like this possible?<br>
  How can i do that?</p>
  
  <p>Thanks</p>