Refactor vuex store actions to use async/await

The vuex store actions currently use a callback-based approach to deal with code that needs to execute after a certain action has handled. This can lead to strongly indented code that can be somewhat hard to follow.

Thankfully JavaScript introduced the ✨ magical ✨ feature of async/await as part of ES2017 which allows us to refactor these kinds of constructs into a more simple shape of:

async function foo() {
  try {
    const result = await this.$store.dispatch("someAction")
    // ... Do something with result
  } catch (e) {
    // ... Handle error
  }
}

As the callback approach is spread pretty far across the codebase this will probably take a while to do and an incremental adoption might be advisable.