Add encrypted elements

[jferard]

Probably not easy: the file should be encrypted, and the manifest should contain information on the encryption.

See:

• http://docs.oasis-open.org/office/v1.2/os/OpenDocument-v1.2-os-part3.html#__RefHeading__752811_826425813
• http://docs.oasis-open.org/office/v1.2/os/OpenDocument-v1.2-os-part3.html#__RefHeading__752833_826425813

[jferard]

See: https://stackoverflow.com/questions/62001716/encrypt-a-file-inside-an-ods-archive

Roadmap:

• transfer the responsibility of the manifest to ZipUTF8Writer (putNextEntry(ManifestEntry(...))). ManifestElement is inside the writer, and added on finish method.
• update ManifestEntry to accept crypto info.
• create a module fastods-crypto that creates a new ZipUTF8Writer: 1. encrypt file, 2. update manifest. Dependency to BouncyCastle.

This will improve the design: OdsElements.EMPTY_ELEMENT_NAMES and ManifestElement.ENTRIES should be unified.