Remove Android length warning
Handle incoming long message attachments
Show long download pending status in message bubble
Fix the width of the smallest spinner
Remove Android length warning from HTML templates
Biggest changes forced by this: alt tags for all images, resulting in
new strings added to messages.json, and a new i18n paramter/prop added
in a plot of places.
Another change of note is that there are two new tslint.json files under
ts/test and ts/styleguide to relax our rules a bit there. This required
a change to our package.json script, as manually specifying the config
file there made it ignore our tslint.json files in subdirectories
