Add theme screenshots & make some fields required

- Description, Name & Author is now mandatory
- Add screenshots
- Add dist/images to electron build

src/Themes/data/monokai-ish/index.ts

@@ -1,8 +1,11 @@
 import { IPredefinedTheme } from "../../Themes";
+import img1 from "./screenshot.png";
 
 export const Theme: IPredefinedTheme = {
   name: "Monokai'ish",
   description: "Monokai'ish",
+  credit: "eltea",
+  screenshot: img1,
   colors: {
     primarylight: "#FFF",
     primary: "#F8F8F2",