add depth_image_publisher package

[knorth55]

this PR add depth_image_publisher package.
depth_image_publisher is a package to publish depth image stored in png + 16UC1 format.
you can try the node with following launch

<launch>
  <node name="depth_image_publisher" pkg="depth_image_publisher" type="depth_image_publisher"
        args="$(find depth_image_publisher)/sample/sample_16uc1.png">
    <param name="encoding" value="16UC1" />
  </node>
</launch>