componentWillMount is a deprecated lifecycle method;
componentDidMount should be used to kick off things
like ajax. In the case of the _App hierarchy, a promise
chain is used to perform initialization, and it is
first started in the constructor by initializing
storage. However, by the time storage is initialized,
resolving the first promise, _App has already mounted.
So, move it all to the componentDidMount lifecycle.

It's a separate view (on the native side) and app (on the JavaScript side) so
applications can use it independently.

Co-authored-by: Shuai Li <sli@atlassian.com>
Co-authored-by: Pawel Domas <pawel.domas@jitsi.org>