adding Util::Assert and tests

@drsnyder @pchojnacki 
implementation of guideline helpers described in https://github.com/Wikia/guidelines/pull/43. ```Assert:::boolean``` will log an error to Elasticsearch and hard fail when the checked boolean is false.
I guess there's no harm in adding a custom AssertionException here, though i think it'd be the exception that the catcher will return a 500-level response. Throwing the exception takes care of that for us.