Add featured label on featured blogs. Fix #351

[nishantn31]

Issue - #351

Changes -

• Added featured label with icon on featured blog posts

Let me know if I need to change the icon or do any other customizations.

[nishantn31]

Thank you! @thibaudcolas May I know when this feature will be deployed and will these changes appear on live site?

[laymonage]

@nishantn31 pretty sure it's live now :) https://wagtail.org/blog

[nishantn31]

Yes I can see that now😍 Thanks for deploying my contribution!