Application schema changes

[awwx]

Applications can change over time (or, especially during development, we might use entirely different applications on the same domain such as localhost:3000). An application can thus start up with old subscriptions, method calls, and documents active in the browser database which aren't compatible with the new application that is running, or with the new version of an updated application.

Have some mechanism to handle resetting or migrating the database when the application or application version changes.