0.6.1: Wad creation fix

Fixed two critical bugs with wad creation:

1: Sub-directories within the wad were not visible to the game.
This was caused by www saving directory slashes in the wrong direction (eg; dir\file should have been dir/file)

2: Dummy/empty files were not being extracted correctly, meaning they wouldn't be re-added to the wad.
This is because I was stupidly adding 'DUMMY_' to the start of the filename.

This means that you can now recreate wizard101 and pirate101 root.wad, without causing any (known) issues in either game.