Add the option to use a folder of gamecube saves instead of a memcard image [issue 6599]

Delroth requested this feature back in sept as [issue 6599](https://code.google.com/p/dolphin-emu/issues/detail?id=6599)
This includes the feature to create a virtual memorycard from a folder of gci files.
The saves that have been written to during gameplay will be stored in the savestate.

On first use of the option the users memorycard will be migrated to a folder (leaving the original memcard untouched)
After the memorycard folder exists, the user is required to synchronize the folder with a memcard image if wanted

commit includes the changes from PR 226