Browse: add prev/next values for browsing forward/backward

Purpose/Overview:

In current implementation - for forward the previous value is null, for backward - next value is null. It can be improved by adding this value from the result list, assuming that these queries can be reached after initial request by browsing around.

Requirements/Scope:

1. Add prev/next value for forward/backward browse results
2. Update unit/integration tests

Acceptance criteria:

• Prev/next value is present for forward/backward results