AT-20: adapt pagination

every page of feed (except head) is now a full page, i.e. contains exactly pageSize entries. 
We will also paginate use forward/backward urls.

See comments on previous pull request
I think we should allow for both use cases:
auto-create the entries table for a every feed. This makes using the JdbcFeedStore very easy.
manually pre-create the entries table for every feed. This allows for fine grained control of the table names.