Treat CAB files as containers

**Is your feature request related to a problem? Please describe.**
The contents of CAB files aren't signed.

**Describe the solution you'd like**
The contents of CAB files should be treated the same as in ZIP files. They should be recursively extracted, signed, and re-assembled before the main CAB file is signed.

**Describe alternatives you've considered**
None

**Additional context**
None