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
Split out test-specific and general utility react components too.
And moved our test/legacy* files for the Style Guide into a styleguide/
subdirectory of test/.
I think we'll be able to live in this directory structure for a while.
