Hello!

Here is a patch to hide the header of feeds without any new or immortal items in the plainview newsticker buffer. My use-case is that I'm subscribed to a lot of low-key feeds that are not updated often, so most of the time, the visible part of a fresh plainview buffer is just a list of empty feeds. This patch adds a new user option `newsticker-hide-old-feed-header-in-newsticker-buffer` which when set to `true` hides them, only leaving feeds with new items visible.

What do you think?

Regards,
Baptiste Strazzulla