Rework the settings dialog.
Add an option to strip invisible images.

By default this option is not set.  If it is set, all invisible
images, i.e. images with a height or width of 0 or 1, will be removed
from the feed item content.
Make it optional to display images.
Merge branch 'images' of git://github.com/michael-k/ttrss into michael-k-images
added changed-signals for the new settings
Merge branch 'michael-k-images'