TPreview shows @mention as link to profile

[sftyzxg]

Text @alexrazbakovwill be rendered as a link: @alexrazbakov in TPreview Add 'markdown-it-mentions' plugin.

Closes #322

[sftyzxg]

Here is the test link for reference. https://63d41386200e2d26400861fd--wedance-sftyzxg.netlify.app/test/