"Mode" GUI option in ShadowSocks Local

[Ultranium]

It would be great to have the "Mode" GUI option for ShadowSocks Local plugin. It already exists for ShadowSocks Server, and it's the same mode option in config file, so copy and pasting it from the Server part should work. This setting is needed to enable UDP proxying, which is disabled by default.

I tried to add "mode":"tcp_and_udp" to the /usr/local/etc/shadowsocks-libev/local.json, and it works just fine, the only problem is that after reboot this file is rewritten with this line removed.