Implemented resource description. 

It may be unstable, I have not tested it yet.

- \Control\Upload : cleaned up some code and added a new method
   - added getUploadFormData() method.

- \Entity\Resource : added code to implement resource description.
Implemented downloads counter.

- resourcePage.js : added downloadLinkBehaviour(). 

- \Control\Resource :
  - Added incrementDownloads() method.
  - controlResource() changed, it should be clearer now. 

- \Foundation\Resource:
  - Fixed a bug in getById(). The \Entity\Resource created has an incorrect $uploadingDate type. It was a string instead of a DateTime object.
  - Added updateDownloadsNumber() method.