* Remove unused function
* Rename field
* Change extensionUnloaded trigger function
* Update how extension unloaded content is shown
* Ignore certain errors caused by extension unload
* Add _showExtensionUnloaded function
* Wrap internals of updateOptions
* Suppress errors caued by extension unload
* Make the frontend trigger the popup's extensionUnloaded event
* Refactor searchQueryUpdate action
* Use standard message handler style
* Use name "promiseOrResult" for consistency
* Use standard message handler convention for Yomichan message handlers
* Use common message handler invoker
* Move "yomichan" object setup to a separate file
* Update script imports
* Align message handlers
* Rename Yomichan.prepare to Yomichan.ready
* Add new prepare function
* Improve isExtensionUrl
