Encrypted disk now decorates another disk

[JaZo]

Description

The encrypted disk now decorates another disk. This allows you to easily encrypt S3, (S)FTP, or any other disk. Even other custom disks!

Motivation and context

Closes #7

How has this been tested?

Updated and new tests

Types of changes

What types of changes does your code introduce? Put an x in all the boxes that apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have read the CONTRIBUTING document.
• My pull request addresses exactly one patch/feature.
• I have created a branch for this patch/feature.
• Each individual commit in the pull request is meaningful.
• I have added tests to cover my changes.
• If my change requires a change to the documentation, I have updated it accordingly.