Add pattern for per-device settings

[Rory-Reid]

Some feedback I got was that it would be useful if the rats list didn't reset the filters each time you navigate away from it. While I want to introduce a simple and advanced rats list to separate "Get me the important stuff" versus "Let me browse my data" it is currently a pain and I was happy to change it.

Today, I'm resolving that by keeping the state in memory, so it resets on app reload now. I aren't fully satisfied with this, but I don't believe it belongs in the database. I considered using localstorage only to find out it does not persist on app restart.

There's some inbuilt MAUI APIs to assist here. You can store preferences and similarly secure settings