Add config option to set the HTTP redirect code for external icons

[jjlin]

The default code is 307 (temporary) to make it easier to test different icon services, but once a service has been decided on, users should ideally switch to using permanent redirects for cacheability.

[BlackDex]

I'm not sure, but won't a 301/308 cause browser to never recheck that specific url again? It will probably depend on the caching of the browser. But it could cause an issue that you can't easily switch to a different icon provide once activated?

[jjlin]

I'm not sure, but won't a 301/308 cause browser to never recheck that specific url again? It will probably depend on the caching of the browser. But it could cause an issue that you can't easily switch to a different icon provide once activated?

Yes, so as mentioned in the doc comments, configuring a 307 redirect is useful if you're testing different icon services. Clearing the browser cache should clear the 308 caching as well, so it shouldn't be that hard to get around.

It's certainly an option to make a 307 redirect the default to make it easier to test different icon services out of the box, but it probably means most users will never know or bother to set the 308 redirect in that case. I could very well be wrong, but I suspect most users interested in an external icon provider will just pick the one they perceive to be most trustworthy, see that it works, and move on.

So I'm not sure there's clearly a best default here. I don't feel that strongly about it though, so if people think 307 is a better default, that's fine with me.