This commit adds a tippy tooltip for inline image previews in messages.
There exists some (reasonable) logic in `static/js/util.js` which
overrides all title attributes for links to user-uploaded content to
ensure they always display "Download <filename>". This doesn't make
sense for inline images specifically because they will be opened in a
ligthbox, so we prevent that.
There is an additional tippy instance created in `static/js/tippyjs.js`
to add tippy tooltips to inline images, which takes advantage of the now
preserved title attribute of the parent link.
Austin Riba