Multiuser plugin, creating unnecessary identities even i have not requested this

### Step 1: Please describe your environment

* ZeroNet version: 4473
* Operating system: W10 and Raspbian
* Web browser: FF
* Special configuration: Multiuser plugin

### Step 2: Describe the problem:

I think Multiuser plugin is creating identities that i have not requested. In my users.json file i found 3222 times phrase: "master_seed": "
On my new ZN instance, i found it 9 times and the "Change account:" prompt on ZeroHello shows only 6 accounts to choose from.
The /Stats page does not show any information about the users.json content so i can see which identity has how many sites, made how many posts or such. Or even the button to delete the identity - but that would be better for some identity manager/switcher GUI - current identity switcher not good when you have many identities - you can not see it on one page and search thru it.

Can the plugin be fixed so it does not create unnecessary identities at the first place?

I am asking because i was bothered with unreliability of the Multiuser plugin (it changing my identity from time to time) so i disabled it (just by renaming its directory) on my new instance where is 9 identities, but Zeronet was not starting without any indication in the log files. So i guess i have to somehow manually edit the users.json file and discover which identity to leave, but i do not remember where i posted or such to pick right identity "block" to leave.

まず Multiuser プラグインの動作を再現し、users.json を Change account プロンプト、/Stats ページ、起動ログと併せて調査します。ID が予期せず作成または選択される理由を特定し、その後、プラグインを無効にして既存の ID を管理しても、起動が妨げられたりアカウント情報が非表示になったりしないことを確認します。

索引モデルが issue の本文から書いたものです。