BG4 plugin fix & BackwardLz77 logic revert

[SomeKitten]

The BG4 plugin's saving feature was completely non-functional from my testing with Superstar Saga DX / Bowser's Inside Story DX as I reported in #295

Two changes:

• I made the paths used when saving relative which fixed name and hash discrepancies.
• I'm not entirely familiar as to why the BackwardLz77 encoding/decoding was changed previously, but reverting those changes seems to fix issues with the BG4 plugin. This algorithm is also used by the HpiHpb plugin, so I have a feeling that the revert may also fix issues with that plugin if they occurred. The alternative is that this change would break that plugin which may be concerning. Since the plugin was last update before the original BackwardLz77 rewrite, I am inclined to believe that it should work with my revert.

I highly recommend that someone who has access to HpiHpb files use the plugin with the reverted algorithm to make sure it is functional with the changes!!

If preferred, I can split this into two PRs, but I figured its alright for this to be one PR.