Make attachment thumbnails fully responsive
Make attachment thumbnails fully responsive

The thumbnails for attachments below a post is responsive.
But there is also a max line length of 5 specified in the
code, blocking nice reordering for smaller screens.

Fixes #6443

Signed-off-by: 01e908796ff33b2313d28eb51e927f3fdf828dbd@gmail.com

StealthWombat/SMF2.1-more-forkery,StealthWombat/SMF2.1-more-forkery