refactor frontend

[Xiaoyang-Gu]

Fixes : [#80 ]

Description :

• Fixed the latest pr [#86 ] for better reviewing. You can check casbin-dashboard for this modified code.

• fix #69 #84 #82 #71 #69 #58

• The Policy Page still needs to enhance. Add Editor like

• Needs syntax and semantics check in add and edit pages.

Screenshot of changes :

Please ensure Checkmark the following :

• [x] - Tested Localy
• [x] - Checked in IE11 and Firefox
• [ ] - Checked in mobile
• [x] - Backend work
• [x] - Frontend work
• [x] - Bug Fixes
• [x] - Enhancements

[hsluoyz]

Don't show Update App.css Signed-off-by: 顾晓阳 <guxiaoyang@bupt.edu.cn> in commit message.

[hsluoyz]

@BetaCat0

[hsluoyz]

Please fix only one issue in one PR.

[Xiaoyang-Gu]

@hsluoyz OK

[andyyumiao]

@hsluoyz OK

Do you have documentation for the web system？