Convert to typescript

[Urhengulas]

why?

This repo will be the starting point for many KaiOS projects and people will mostly just adopt the used packages and versions.

impact

Therefore converting it to typescript will result in better and more stable KaiOS apps in the future.

(Happy to make these changes)

[Urhengulas]

@seinlin Did you give it a thought?

[seinlin]

@Urhengulas, you are more than welcome if you can send a pull request. Thank you.