Ask user to download block lists when enabling adblocker for the first time

[jroovy]

Is your feature request related to a problem? Please describe.
Fulguris doesnt automatically download or ask the user to download adblock lists when enabling it on a fresh install. This made me frustrated trying to figure out why the ad blocker isn't working after enabling it.

Describe the solution you'd like
When turning on adblocker for the first time, ask the user if they want to download the block lists.
A pop-up window asking the user should be effective at getting their attention.

App version: 1.9.30 (f-droid version)