Move state and component login into the component

[ebebbington]

Summary

First we need to extend DestinyElement, but to do so destiny needs to proivde typings

Then, all our logic around handling data eg in the call component, we add html in a separate function, would instead be replaced by something like:

extensions = reactive([])

template = xml`
  ...
  ${this.extensions.forEach(ext => xml`<option>...`)}