Add the code block button click copy function

[liuyingqiao2019]

In order to copy the code better, I added the code block button click copy function, and it adapts to all modes. This submission solves the problem of version conflict of jquery files between codes. When selecting a long code with only one line, this copy button will obscure the last few words of this line of code. Therefore, I changed the position of the copy button in the second submission so that the last word will not be blocked.

[Stark-X]

• 去除不需要的 jquery 引用（原来就有用到）
• 去除复制粘贴的 webpack 代码、重构
• 样式优化，hover 显示复制按钮，而不是 hover 显示提示文字
• 按钮的出现效果改为正确的渐隐渐出