Added a new method to the web service to vote

Vote can now be commented with the new method of the ProjectRestService.
A new JSON object is used to perform the vote. This new method is not
yet used by the web client (next step).
Vote can now be commented via the web interface

Added the comment text box to comment a vote.
Removed Id from Vote embedded entity

Id in Vote entity was not used (since it is embedded) an has been
removed.