refactor(qavatar): use composition API

[IlCallo]

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Documentation
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• It's submitted to the dev branch and not the master branch
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix: #xxx[,#xxx], where "xxx" is the issue number)
• It's been tested on a Cordova (iOS, Android) app
• It's been tested on a Electron app
• Any necessary documentation has been added or updated in the docs (for faster update click on "Suggest an edit on GitHub" at bottom of page) or explained in the PR's description.

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information:
No noticeable differences between JS or TS build, just the build time increase.
I guess we'll see them diverge as we proceed into migrating stuff to TS.
The resulting JS build size will slightly increase as there will always be a new composable for every mixin (even if the mixin will share the logic from the composable), but most of them will be tree-shaked away I guess

Seems like the buiild time increase is all due to type-checking.
Disabling type-checking reverts to 40-50s the build time.
Of course, disabling type-checking is not what you want, right after adding TS to your project, but Vue too disable it for dev builds and only enable it for prod builds, so they must have the same problem

Their rollup config: https://github.com/vuejs/vue-next/blob/master/rollup.config.js

They are also using the microsoft api extractor to extract and generate their type defs automatically (we might not want to do that right away) https://github.com/vuejs/vue-next/blob/master/scripts/build.js#L102