Excluded WEB-INF from installer, dist size reduced by one third. Dev doc added. Misc cleanup.

war/package.json

 {
   "name": "draw.io",
-  "version": "6.2.4",
+  "version": "6.3.1",
   "description": "draw.io desktop",
   "main": "electron.js",
   "scripts": {
@@ -24,9 +24,9 @@
   "homepage": "https://github.com/jgraph/draw.io",
   "dependencies": {
     "electron-log": "^1.3.0",
-    "electron-updater": "^1.8.2"
+    "electron-updater": "^1.8.3"
   },
   "devDependencies": {
-    "electron": "^1.6.2"
+    "electron": "^1.6.3"
   }
 }
\ No newline at end of file