PostMessageTransportBackend and Transport, along
with the constants file they both use, were
moved int js-utils for jitsi-meet-spot.

It has been around bor > 2.5 years already.

* 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.

Improves naming.
Fixing typos.
enableLegacyFormat param was working like disableLegacyFormat.
Improves the structure of transport/index.js

For lack of a better word/phrase, I'm calling all changes coding style.
I'm targeting readability through naming and syntax.

The transport module will be handling all external app
communication.