* feat(analytics): move to React

The analytics handlers have been moved to JitsiMeetGlobalNS, so now they are
stored in `window.JitsiMeetJS.app.analyticsHandlers`.

The analytics handlers are re-downloaded and re-initialized on every
lib-jitsi-meet initialization, which happens every time the config is changed
(moving between deployments in the mobile app).

* Adds legacy support for old analytics location.

Avatars are cached to the filesystem and loaded from there when requested again.
The cache is cleaned after a conference ends and on application startup
(defensive move).

In addition, implement a fully local avatar system, which is used as a fallback
when loading a remote avatar fails. It can also be forced using a prop.

The fully local avatars use a user icon as a mask and apply a background color
qhich is picked by hashing the URI passed to the avatar. If no URI is passed a
random color is chosen.

A grace period of 1 second is also implemented so a default local avatar will be
rendered if an Avatar component is mounted but has no URI. If a URI is specified
later on, it will be loaded and displayed. In case loading the remote avatar
fails, the locally generated one will be used.