Sessions

[rockwellll]

This PR improves session generation and offloads the work from a client-server approach into a client-only approach.

Todos

• Publish a new version to npm.

Session generation

Previously, generating a session would have to go to Hellotext's servers to create a new one. This induced latency to the package's initialization time because it would have to wait until Hellotext replied with the session's token. Now, a session is generated on the client when is not present, this

1. Reduces the wait-time for booting the lib by shaving the request to Hellotext when no session was found.
2. Simplifies session generation across all devices.

The new session generation algorithm reuses crypto.randomUUID() which has now full support across all major browsers and can safely be assumed available everywhere.

Refactors

Moves session initialization code from Hellotext into a dedicated Session model that is responsible for setting the session, as well as dispatching events to subscribers. This solves a race-condition if a user had accessed Hellotext.session in a on-session callback because the subscriber would have been notified before Hellotext.session being set.