View, status.tx: implement rendering media entity images.
View: now it shows both entities.media and extended_entities.media.
status.tx: use one-line syntax for control statements. This improves the rendered HTML.
Manual::Status: comment about entities.media and extended_entities.media.
busybird.css, status.tx: tidy up styles for extension images.
View, status.tx: now media images are obtained via bb_media_image_urls template function.
t/Main_PSGI_View.t: add test for bb_media_image_urls template function.