Cleaning some functions in DAOs and webservices. Deleting useless files.

Adding tag functionalities :
  - friends in friends lists now contain tags, and tags can be changed by sending a friend with a tag list
  - all the tags are visible with a GET at /tags.

Fixes issues #35 , #34 partially :
I think we have to redefine the (client's) need : what services we want/have to offer or not.
cf issues #34 and #35 for more details on what is done.