feat: integration of DAISY Knowledge Base (#41)

Main features:

* DAISY KB source material is included as Git submodule ( https://github.com/daisy/kb/ )
* KB resources are served via an HTTPS server on `localhost`/`127.0.0.1` (self-signed certificate)
* The local server enables HTTP caching, but resources cached/stored for the browsing session are flushed every time the app exits.
* KB webpages are displayed inside Electron BrowserWindows (multiple concurrent ones are allowed)
* This is an exact copy of the online version (i.e. styles / visual branding, information structure, etc.)
* External links (i.e. outside of `localhost`/`127.0.0.1`) are loaded in the user's registered web browser.
* A "go online" link is dynamically injected in each visited local/offline webpage, so that the user can decide to browse the live web version at any point in time.
* The application top-level menu bar contains menu items to directly access the root of the KB (offline, and online versions).
* The reports generated by Ace 'core' contain HTTP online KB links, but these are intercepted so that the user reaches the local/offline first.

Additionally:

* Added missing copy/paste/select-all commands in menu bar(s)
* Fixed keyboard shortcuts (MacOS vs. Windows/Linux key modifiers)
* Fixed drag and drop for hyperlinks (not files)
* Fixed issues related to managing the application state with main Electron window vs. secondary ones (e.g. about box, and KB browsers).
* Fixed main window positioning on Windows (maximized state is now correctly unmaximized)

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "kb"]
+	path = kb
+	url = https://github.com/daisy/kb

README_KB.md

@@ -0,0 +1,12 @@
+# DAISY Knowledge Base
+
+Deployed website:
+https://kb.daisy.org/
+
+Source GitHub repository (master branch):
+https://github.com/daisy/kb
+
+Git submodule revision:
+8bbd34fb44c7b2bdcd7f1886c03355183209b5b4
+https://github.com/daisy/kb/commits/8bbd34fb44c7b2bdcd7f1886c03355183209b5b4
+https://github.com/daisy/kb/compare/8bbd34fb44c7b2bdcd7f1886c03355183209b5b4...master

package.json

@@ -2,7 +2,7 @@
   "name": "ace-gui",
   "productName": "Ace by DAISY",
   "description": "Ace, the EPUB accessibility checker by the DAISY Consortium (desktop application)",
-  "version": "1.0.0-beta.0",
+  "version": "1.0.0-beta.2",
   "author": "DAISY Consortium",
   "homepage": "http://daisy.github.io/ace",
   "repository": "daisy/ace-gui",
@@ -43,7 +43,7 @@
     "clean": "cross-env BUILD_TARGET=clean node build/build.js",
     "build:bundle": "webpack --config=build/webpack.app.config.js --env=production",
     "build:chromium": "cross-env BUILD_TARGET=fetch-chromium node build/build.js",
-    "build": "yarn build:bundle && electron-builder",
+    "build": "yarn build:bundle && cpy --cwd=\"./kb\" --parents \"**/*\" \"../app/kb/\" && electron-builder",
     "postinstall": "electron-builder install-app-deps",
     "release": "build -mw -p always",
     "start": "node build/start.js",
@@ -54,12 +54,14 @@
     "@daisy/ace-core": "^1.0.2",
     "@material-ui/core": "^3.0.0",
     "@material-ui/icons": "^3.0.0",
+    "@mrmlnc/readdir-enhanced": "^2.2.1",
     "about-window": "^1.12.1",
     "electron-debug": "^2.0.0",
-    "@mrmlnc/readdir-enhanced": "^2.2.1",
     "electron-redux": "^1.3.1",
+    "express": "^4.16.4",
     "fs-jetpack": "^2.1.0",
     "jszip": "^3.1.5",
+    "portfinder": "^1.0.20",
     "prop-types": "^15.6.2",
     "react": "^16.3.0",
     "react-dom": "^16.2.0",
@@ -69,17 +71,21 @@
     "redux": "^4.0.0",
     "redux-promise": "^0.6.0",
     "redux-thunk": "^2.3.0",
+    "selfsigned": "^1.10.4",
     "tmp": "^0.0.33",
-    "typeface-roboto": "^0.0.54"
+    "typeface-roboto": "^0.0.54",
+    "uuid": "^3.3.2"
   },
   "devDependencies": {
     "@babel/core": "^7.0.0",
     "@babel/preset-env": "^7.0.0",
     "@babel/preset-react": "^7.0.0",
+    "@types/express": "^4.16.1",
     "babel-loader": "^8.0.2",
     "babel-plugin-transform-class-properties": "^6.24.1",
     "babel-plugin-transform-object-rest-spread": "^7.0.0-beta.3",
     "chalk": "^2.4.1",
+    "cpy-cli": "^2.0.0",
     "cross-env": "^5.2.0",
     "css-loader": "^1.0.0",
     "devtron": "^1.4.0",