importfeed: Display feed title

importfeed: Display feed title

When importing a bunch of feeds, this makes it more clear what it's working
on. Also, I sometimes want to delete a particular feed from a list of feeds
but don't know which url belongs to the feed, and this solves that.

Control characters are filtered out just to protect against some feed
putting escape character stuff in the feed, which could be a
security problem. (Control characters also get filtered out of
importfeed filenames.)

Sponsored-by: Luke Shumaker on Patreon