Discussion Dao made #2
DiscussionService is made #2
DiscussionDao stub is made #2
DiscussionDao is made #2
test version of link to next discussion table and to previous discussion table is made #2
apply code review #2
apply code review #2
apply code review #2
Merge pull request #19 from tAsktoys/DiscussionDaoImplement

Discussion dao implement