Create initial app loading screen

[taoeffect]

Problem

In PR #1521, to address #1765, @corrideat added this v-if to the router in frontend/index.html:

<router-view v-if="ephemeral.ready" class="l-page"></router-view>

This causes a blank white page to appear on initial page load for a bit.

Solution

Create a v-else and set it to a page that shows a simple loading page to indicate that the app is loading.

Create a branch off of master (by the time you see this issue Sebin, e2e-protocol should be merged)

[SebinSong]

Hey @taoeffect @corrideat,
it's just a question out of curiosity but why did ephemeral.ready need to be set up this way (below) instead of definitng it in data () { ... } block and then doing this.ephemeral.ready = true?

...
}).finally(() => {
  Vue.set(this.ephemeral, 'ready', true)
})
...

[taoeffect]

@SebinSong That's a good question. While I can't speak for @corrideat I think there's no reason why you couldn't do it that way. In fact I think that would be better as it's more idiomatic.