Apply paging properly on user activity list
Switch back to using offset/limit as opposed to page/count.

 - Changing to explicit paging in the first page was a Bad Call™
 - Having offset indendent of count allowed doing this like fetching
   one more item then needed to check for more content on unbounded
   streams. This is not possible when offset is calculated via page
   and limit.
 - It is unnatural to use paging on unbounded streams
 - It was needlessly different to RMDBS standard practice
Merge pull request #62 from mikesname/rest_paging

Changes to how paging is handled on the web service