Allow for the creation of aliases

[agsimmons]

Thanks for the extension :)

Coming from DuckDuckGo, I've found myself wanting to create aliases for certain websites.

For example, for amazon.com I would like to register the !a and !az bangs, but use the same search URL for both. To do this currently, I would need to add a new entry for az and copy and paste the URL from my existing entry. This isn't a huge deal, but having them linked would allow for updating the URL in a single place if needed instead of for both bangs.