Add elfeed-search-title-face and elfeed-search-unread-title-face

[yuezhu]

This PR adds elfeed-search-title-face and elfeed-search-unread-title-face, which are used to show feed's title in Elfeed search buffer.

Both faces were unspecified in zenburn, and the default is a bit too bright, and not distinct enough for read and unread feeds.

After my change:

• [x] The commits are consistent with our contribution guidelines
• [x] You've added a before/after screenshot illustrating visually your changes.
• [ ] You've updated the changelog (if adding/changing user-visible functionality - e.g. theme new faces/packages, changing existing faces, etc)
• [ ] You've updated the readme (if adding/changing configuration options)

Thanks!

[bbatsov]

Thanks!