[#855] Pagination support for data > monitoring tab
[#855] Resets the `since` property when moving between tabs

* If you have data in the "Inspect Data" tab, the property `since` gets
  a cursor value. If you move to the "Monitoring" tab, select a survey
  group and click the "Find" button, the cursor from the "Inspect Data"
  query is used, resulting on an error
[#855] Refactor based on feedback from @iperdomo
Merge pull request #862 from akvo/feature/855-missing-pagination

[#855] Pagination support for data > monitoring tab