Refine Markdown Editor

Recycle Bin

Now recycle bin is just a simple folder. No corresponding node for it.

Quick Access

Support removing items from Quick Access directly.

Markdown Editor

Read Mode

• Support centering images
  
• Add user.css for user styles. User could edit this file to quickly modify the styles of read mode.
  
• Support debugger via F12
  

Edit Mode

Support context-sensitive context menu such as copying images or opening links.