Also update tests

Allows for simpler code, especially making `getReservedNick` easier to override

`initializeDisco` already gets called upon reconnection which
accomplishes this.

- Add `onReconnected` method for chatboxes to clear messages
- Move MAM models to headless build.
- New event `onChatReconnected`

- Save date for older message versions and display it in the modal
- Properly handle the correction being received *before* the corrected message

Fixes #1577

Otherwise we can get into a situation where Converse stops trying to
reconnect.

so that they're cleared when the last tab closes

fixes #1571

Helps with enforcing discipline of keeping them separate