Added '.NET Transactional File Manager' support, removed our implementation

Closes #161 
Uh oh, we already have a method for doing this. `GenerateDefaultInstall()`. It's not the same as all the files in the archive; instead, we look for the top-most directory that has the same name as the module identifier, and install that.

This is really my fault for not factoring out all the code into something which lets you supply a module and a zipfile, and get back the files which would be installed. (That was kinda what `FindInstallableFiles()` was meant to do, but it existed before we had default installs).

I'll be sending you a PR on your PR, but it should be a pretty straightforward one. :)

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