GitLab

- Restore Gravatar functionality
- Add new button for "Use Initials"
- Set both buttons to use text-left class
- Update toast property autoClose to duration (wrong library, my bad!)
- Update toast messages to clarify that this isn't "Gravatar" but "avatar"
- Add i18n text to en-US/translation.json

Browsers and plugins that spoof canvas data produce corrupt images. In attempt to mitigate:

* Add canvasPixelTest() to test a single pixel and test the RGB values
* Test canvasPixelTest() inside generateInitialsImage() and use default `/user.png` if failure detected
* Call canvasPixelTest() directly within settings to avoid setting an invalid image
* Use toast.error() with 10 second autoClose

Translation values for en-US are not necessary, the keys will be
used as fallback.