inbox: Change empty-inbox text so it links to "Combined feed" and "Channels" #1553
Description
This issue is blocked on #1285.
With #1552, we'll have some plain text as a placeholder when the inbox is empty:
We should change it to say something like:
There are no unread messages in your inbox. You might be interested in Combined feed or Channels.
except instead of italics, we put links to those pages. (And/or to "Recent conversations", which isn't implemented yet; that's #315.)
Putting inline links in prose is blocked on getting it to work with internationalization; that's #1285.