Started implementing resource description.

Added description field on resource upload.
Fixing and cleaning code.

- \Control\Upload : 
   - Reviewed handleUpload(). 
   -  Added validateFormInputData() method.

- upload.js : Fixed a little bug and moved some code in handleUploadButton().
Fixed a bug in resources rating.

Average of votes was wrong because of a bad votes count. The problem was in \Entity\Resource::updateQualityScore() and in \Entity\Resource::updateDifficultyScore(). It was not necessary to pre-increment the votes count.