Refactor AnsweredCalls analyses

New helper modules for private methods in classes. Queri::Stats now defines
constructor methods and attr_readers.
Refactor AgentsAndSessions analysis

Use new helper code to simplify analysis class.
Refactor DetailsOfAgentSessionsAndPauses classes

Use new helpers, and add CompositeAgentLevelReportHelpers module, to simplify
analyses of DetailsOfAgentSessionsAndPauses.
Merge branch 'detail_agent_sessions'
Rename report class to follow convention