Sigmon 152 ipq query fails

Context

• https://its.cern.ch/jira/browse/SIGMON-152

What was done

• ipq_query.query_pc_pm_with_source now checks for empty timestamp
• Added tests for ipq_query.query_pc_pm_with_source

Review objectives

• assessment of code functionality
• assessment of code quality
• identifying potential refactorings / logic common to other projects
• knowledge sharing
• should we export functions like check_warnings and check_empty_dfs to another module and use them in all the tests?