* Add url/voice options to audio sources
* Add help for TTS
* Remove old settings
* Update tests
* Update use of audio source URL
* Improve labels for sources with the same type
* Update environment info to return the 'safari' browser
* Fix popup display on Safari
* Update environment assignment
* Add data-loading-stalled property when loading takes longer than expected
* Add notification when loading has stalled
* Allow getDictionaryInfo invocation on non-privileged contexts
* Update _validatePrivilegedMessageSender
* Don't listen to 'voiceschanged' event unless addEventListener is present
Also expose an event