This starts moving alerts to the same subsystem where they are relevant
instead of putting everything in notifications.
So far, only the explorer file in use error is handled like this.
This replaces the localStorage file storage with a new backend that uses
localForage (indexeddb) for storing the file contents. This will also
allow storing multiple files.
This is the beginning of the BLE Pybricks service implementation, so
changes are made to get a handle to the Pybricks control characteristic
and enable notifications.
Currently, only one event (the status report event) and no commands are
implemented on this characteristic.
The new status report event replaces monitoring the UART for >>>>
strings to get the current hub state.
Also includes some minor cleanup in the ble-uart/actions for consistency.