Add partial Flagon logo to UserALE.js browser extension icon

[poorejc]

for branding

[brucearctor]

@poorejc - do you want to be the assignee for things like this? Do we need a bot to auto-de-assign ( or at least message ) if > some time period passes without any action to the issue?

[Jyyjy]

https://github.com/apache/flagon-useralejs/pull/480