bug 1094767; crashstorage type for new ES module

This PR introduces a crashstorage type for the new ES module.  It also modifies the `ConnectionContext` class to bring it in line with the patterns established in the other `external` modules.  The changes to the context required some other modifications to be made to the index creation class (and associated tests).

`r?` @AdrianGaudebert @twobraids 
They belong to different modules, there is no problem with them having the same name. And it's not even the same name, look: ``ElasticSearchCrashStorage`` versus ``ElasticsearchCrashStorage``! ;)