Refactor the retrieval of the word usage examples

[kirlat]

@balmas: I think we should have an issue for further refactoring here. This method is only called if the wordUsageExamplesON setting was set to 'onLexicalQuery'. If it's set instead to 'onDemand', the still-existing LexicalQuery.getWordUsage data method is called instead. As we have discussed previously, I would like for all resource queries to be able to set as 'pre-cache' or 'on-demand' and for that to trigger when they are called, but we should not have two separate methods for calling them depending upon when they are called. This is fine for this PR, but we do need to refactor it.

(see #568 (comment))