feat: add plugin support for freeAccount

[ylfzq]

add support for freeAccount.

Usage:

The config file of 's' server is as below, which is compatible with my previous commit.

type: s

shadowsocks:
  address: 127.0.0.1:12532
  plugin: "obfs-server"
  plugin-opts: "obfs=tls;failover=example.com:80"
manager:
  address: 0.0.0.0:12533
  password: 'yourPassword'

The config file of 'm' server is as below:

type: m

manager:
  address: 127.0.0.1:12533
  password: 'yourPassword'
plugins:
  freeAccount:
    use: true
    port: 12901-12999
    flow: 3G
    time: 8h
    address: 'your.host.or.your.ip'
    method: 'chacha20-ietf-poly1305'
    plugin: "obfs-local"
    plugin-opts: "obfs=tls;failover=example.com:80"
    listen: '0.0.0.0:12534'

I've tested on my server, you can check it again.

Besides, I changed the index.html also in which I downgrade the qrcode errorCorrectLevel for more capacity of characters. A line addded to indicate the softwares can parse the ss URL or scan the qrcode.