add electron build!

- use webpack to build electron-main and electron-preload
- intercept 'https' protocol to run on 'https://replayweb.page' in app
- serve local files from 'https://files.replayweb.page'
- support flash in with service worker replay: catch any fallthrough urls and load via intercept with render process callback
- add icons for electron build

.gitignore

@@ -10,3 +10,6 @@ local-examples/
 .DS_Store
 .sass-cache/
 _site/
+dist/
+!dist/frontend.js
+!dist/embed.js