Upgraded the project to Vue2

[asvrada]

Check each commit for detailed changes.

The original repo fails to serve as a Vue example project for beginners anymore as it's using Vue 1 that are outdated, as well as many other packages. And this PR is aimed to upgrade this project to the most up-to-date state, which includes upgrading outdated packages and fixing incompatible codes that package upgrading brings.

Following are changes other than simple package upgrade:

1. Re-indented all files
2. Renamed text.vue to text-input.vue
3. Using debounce func from lodash now