Consolidate on one error handler

There were a lot of suspicious calls to set_error_handler and restore_error_handler. One of them was clobbering the `onWikiFactoryExecute` call to setup the `WikiaLogger::onError` handler.

This pull request attempts to clean up the calls to `[set|restore]_error_handler` for more consistent handling to ensure more events are passed through `WikiaLogger::onError`.

Related: see this [discussion](https://github.com/Wikia/app/commit/a1f0d54d91e8c476a434ceecb8d74664d3d48622#commitcomment-6492731).

/cc @Wikia/platform-team