offline mode / downloads: remember storage location for downloads

[foss-]

iOS 15.2 Finamp 0.5.1

Currently

When tapping on download icon Add Downloads dialog pops up asking for location to store files. Once the location has been selected and user taps Add files are downloaded. This dance has to be done for every new download.

Expected

Remember storage location for next download. Chances are very high user is going to use the same storage location, so remembering it will make the download dance easier.