Update bass libraries (and add script to ease the update process)

[peppy]

The intention here is to make the process of updating the files easier. The structure of bass archives is all over the place, but the hope is there's some reason to it and this will continue to work going forward. If it doesn't, only minor tweaks should be required.

Notes:

• We are using experimental versions for desktop platforms (where available). These are the /stuff/ URLs. We are doing this because the main reason for upgrading here is deploying changes which are only deployed here (see https://www.un4seen.com/forum/?topic=20482.0 and https://www.un4seen.com/forum/?topic=20589.0)
• The iOS plist files have been updated to match the official version. @frenzibyte would be great if you can check on this briefly.
• I haven't tested these new libraries yet. The plan is to merge this and then do a NativeLibs build for further testing, before doing a full framework release. If it's preferred that things are tested first, I will release a nuget prerelease build for testing prior to merge of this PR.