Implement initial framework for Dolphin importer

- Uses cache reading code from Lutris by strycore. https://github.com/lutris/lutris/blob/master/lutris/util/dolphin/cache_reader.py#L23

flatpak/hu.kramo.Cartridges.Devel.json

@@ -12,6 +12,7 @@
         "--socket=wayland",
         "--talk-name=org.freedesktop.Flatpak",
         "--filesystem=host:ro",
+        "--filesystem=~/.var/app/org.DolphinEmu.dolphin-emu:ro",
         "--filesystem=~/.var/app/com.valvesoftware.Steam/data/Steam/:ro",
         "--filesystem=~/.var/app/net.lutris.Lutris/:ro",
         "--filesystem=~/.var/app/com.heroicgameslauncher.hgl/config/heroic/:ro",