profiles: fix application

moving to a DB meant empty slices in the Configuration & Policy structs
were being stored as null, and striking a nerve with Jellyfin.
Mediabrowser library change fixed that by de-nulling them itself, and a
new bool field called "Homescreen" is now used to decide if a profile
has a homescreen layout stored or not. This field is hopefully correctly
filled in during migration.

migrations.go

@@ -286,6 +286,9 @@ func migrateToBadger(app *appContext) {
 	}
 
 	for k, v := range app.storage.deprecatedProfiles {
+		if v.Configuration.GroupedFolders != nil || len(v.Displayprefs) != 0 {
+			v.Homescreen = true
+		}
 		app.storage.SetProfileKey(k, v)
 	}