水印显示文本修改，添加不可猜测字符提升安全性

[feiazifeiazi]

1. 水印显示文本修改，由之前的display 改为 display+创建日期格式化Hdi。（Hdi：小时,日,分钟）
2. 水印文本这个js变量在浏览器F12里很容易找，很方便被人修改为其他人的名字,进行伪造。添加不可猜测的用户创建日期防止伪造。能接受删除水印，但不能接受伪造水印。

修改后的效果：

修改前的效果：

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.89%. Comparing base (48101d9) to head (99835c1).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2577   +/-   ##
=======================================
  Coverage   76.89%   76.89%           
=======================================
  Files         117      117           
  Lines       16106    16106           
=======================================
  Hits        12385    12385           
  Misses       3721     3721           

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