Separate SASL password and server PASS password options

[usrbinsam]

https://github.com/Throne3d/node-irc/blob/2a5f46d4c1cd7fd7a9929a24bcb9879585b5cd5a/lib/irc.js#L756-L762

In some cases, it's useful to connect with a server password and a SASL password, so it might be useful to have a separate config option for SASL password and server password since they're not necessarily mutually exclusive.

My use case is using the server password to authenticate an I:Line/Auth Block, alongside normal SASL Plain services authentication.