List enhancements

[zhuochun]

Is your feature request related to a problem? Please describe.

Update several paragraphs to a list items. The empty lines is converted to empty list items.

Describe the solution you'd like

Above to automatically remove the empty list items.

Example

Paragraph A

Paragraph B

Trigger Toggle UL now:

- Paragraph A
- 
- Paragraph B

Trigger Toggle UL expected:

- Paragraph A
- Paragraph B