When calling `getDeviceList`, wait for the devices to be fetched
Otherwise a race condition might occur, whereby a new device gets
created in the collection, and then removed again as the collection is
replaced with the values fetched from the browser-storage cache.
Also created `converse-omemo-fingerprints` component to asynchronously
render fingerprints in the user details modal. Was done as part of this
commit because due to `getDeviceList` being async, the relevant test for
the modal were also failing
