Turn on all of Microsoft's recommend lint rules

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

ts/test/components/media-gallery/groupMessagesByDate_test.ts

@@ -1,5 +1,3 @@
-import 'mocha';
-
 import { assert } from 'chai';
 import { shuffle } from 'lodash';