Alerts should be stored in an SQLite database instead of in memory

[justdave]

If you choose an entire state or the country, it's a big list of alerts at any given time. Save memory by storing it in a database instead. This also allows a lot of other features on the enhancement request list to be implemented easier (such as alert caching, and early dismissal of non-expired alerts)

[justdave]

My MCStatus app already does this, we can probably lift some of the code from there (convert Java to Kotlin though)

[justdave]

alerts should be stored by widget, since different widgets can have different lists.
when a widgets is deleted, delete all entries in the DB that belong to that widget.
when our periodic timers fire, delete any expired alerts.