Add remember relay options (#1000)

[ThatOneShortGuy]

A fix for #1000

As someone who has never written Go before, that was pretty straight forward

[schollz]

@ThatOneShortGuy the reason they were taken out is because its annoying when the default server relay changes and the config files have to be redone (because it stores the old), so my one ask would be to fix this so that the remember relay option only works if the relay address is different than the default

[ThatOneShortGuy]

@schollz I see what you're talking about. At this point my concern is when the default IP changes. We can't track that in code, and the existing configs already have something like "RelayAddress": "46.62.254.13:9009".

The best solution to that I can think of is to add the default models.DEFAULT_RELAY{6} to the list of addresses to try ([]string{c.Options.RelayAddress6, c.Options.RelayAddress}). I didn't add that in this PR yet, wanted to get your opinion first.

[schollz]

Maybe something like saving the default address as a special symbol "default" or something.

That way when it loads it always knows to use the default (even if it has changed).

[ThatOneShortGuy]

I added the "default" if the saved relay is the same as the relay. However, this gave me the idea to make the saved relays work correctly by having a prefixed token "non-default:". This way, it will only work on relays user have saved after updating to maintain backwards compatibility.

[schollz]

Awesome, looks good!