Add support for Shift+Enter key, used to add new line in codeblocks if they in lists

[TitovLab]

Unable to add new line in code block if it is inside ordered or bullet list, for example try press Enter inside code block to add new line between first and third line:

  - First item<code>
First line
Third line
</code>
  - Second item
  - Third item

This pull request adds Shift + Enter key to add new lines inside code block.

[annda]

Thanks for submitting. Please check the build error message and fix the code style errors.