Add basic compatibility with IMGAPI v2

Changes include : 
 * s/datasets/images/g
 * s/\"/\'/g
 * ping/pong compatibility
 * sending dataset logic
 * Added Content-MD5 header

Your templates have to be in this form : 
```
<serve_dir>
               \  <dataset - uuid>
                                       \ - file
                                       | - manifest.json
```