Demo app in Vue

[asharghi]

Added a demo app in Vue as promised in #83

[RobertGardner]

Thanks for doing this!

app.js seems to be missing (.gitignore ignores all .js files unless they are explicitly added)

In src/package.json you should add these scripts:

    "demo-vue.ios": "npm run tsc && cd ../demo-vue && tns run ios --emulator",
    "demo-vue.ios.min": "npm run tsc && cd ../demo-vue && tns run ios --env.uglify --emulator",
    "demo-vue.ios.ci": "npm run tsc && cd ../demo-vue && tns build ios --env.uglify",
    "demo-vue.android": "npm run tsc && cd ../demo-vue && tns run android --emulator",
    "demo-vue.reset": "cd ../demo-vue && npx rimraf -- hooks node_modules platforms package-lock.json",

and change the clean script to:

    "clean": "npm run demo.reset && npm run demo-angular.reset && npm run demo-vue.reset && npx rimraf -- node_modules package-lock.json && npm i",

Making those changes, I was able to get this demo to run. Cool!

One enhancement I'd like to see before merging, though, is to display the currently selected Payment Type, Shipping Method, and Total since otherwise it's confusing. (Displaying the info in the Debug area as is done in the other demos would be nice, too.) Finally, the price (to the right of Something to Buy) is off by 100. (The price is in pennies.)