Recommendations: code cleanup + debug logging
DataMartService: add a fallback when replication does not work

Hide getTopArticlesByPageview method behind a helper that performs a fallback to the last known rollup

A Nasty And Ugly Hack (TM) before we have a proper rollups solution.

@see https://wikia-inc.atlassian.net/browse/OPS-5465
fix indentation issues
Merge pull request #5684 from Wikia/CON-2328-recommendations

CON-2328: DataMartService: add a fallback when replication does not work