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';
 

ts/test/html/index_test.ts

@@ -1,4 +1,3 @@
-import 'mocha';
 import { assert } from 'chai';
 
 import * as HTML from '../../html';
@@ -52,6 +51,7 @@ describe('HTML', () => {
       {
         name: 'URLs without protocols',
         input: 'github.com',
+        // tslint:disable-next-line:no-http-string
         outputHref: 'http://github.com',
         outputLabel: 'github.com',
       },

ts/test/tslint.json

@@ -0,0 +1,11 @@
+{
+  "defaultSeverity": "error",
+  "extends": ["../../tslint.json"],
+  "rules": {
+    // To allow the use of devDependencies here
+    "no-implicit-dependencies": false,
+
+    // All tests use arrow functions, and they can be long
+    "max-func-body-length": false
+  }
+}

ts/test/types/Attachment_test.ts

@@ -1,7 +1,3 @@
-/**
- * @prettier
- */
-import 'mocha';
 import { assert } from 'chai';
 
 import * as Attachment from '../../types/Attachment';

ts/test/types/Contact_test.ts

@@ -1,4 +1,3 @@
-import 'mocha';
 import { assert } from 'chai';
 
 import { getName } from '../../types/Contact';

ts/test/types/Conversation_test.ts

@@ -1,4 +1,3 @@
-import 'mocha';
 import { assert } from 'chai';
 
 import * as Conversation from '../../types/Conversation';

ts/test/types/Settings_test.ts

@@ -1,11 +1,11 @@
 import os from 'os';
-import sinon from 'sinon';
+import Sinon from 'sinon';
 import { assert } from 'chai';
 
 import * as Settings from '../../../ts/types/Settings';
 
 describe('Settings', () => {
-  const sandbox = sinon.createSandbox();
+  const sandbox = Sinon.createSandbox();
 
   describe('isAudioNotificationSupported', () => {
     context('on macOS', () => {

ts/test/types/message/initializeAttachmentMetadata_test.ts

@@ -1,4 +1,3 @@
-import 'mocha';
 import { assert } from 'chai';
 
 import * as Message from '../../../../ts/types/message/initializeAttachmentMetadata';