Added "createUser" JSON RPC

[fraggerfox]

1. Fixed a possible bug where the "login" RPC call would not allow the login to not happen because a user session does not exist, current code allows the "login" function to be a pass-through hence generating a proper session cookie which can be used for further authenticated transactions via the RPC API.
2. Added a "createUser" RPC for remotely creating users using JSON RPC API for DokuWiki.

• Example JSON Request to create a user

  {
  "jsonrpc" : "2.0",
  "id" : "webClient",
  "method" : {
    "methodName" : "dokuwiki.createUser"
  },
  "params" : [
    {
      "string" : "testUser"
    },
    {
      "string" : "password"
    },
    {
      "string" : "testUserName"
    },
    {
      "string" : "test@example.com"
    }
  ]
  }
  

• Response (For success)

  {
  "jsonrpc" : "2.0",
  "id" : "webClient",
  "result" : 1,
  "error" : ""
  }
  

• Response (For Failure)

  {
  "jsonrpc" : "2.0",
  "result" : "",
  "error" : {
    "code" : -32603,
    "message" : "Invalid E-Mail"
  },
  "id" : "webClient"
  }