Implement conversion of `.webarchive` files to HTML

[gy-mate]

Description

.webarchive files generated by Safari cannot be imported.

Version

2.0.2

Preferred solution

Pre-convert .webarchive files to HTML + assets.

Might try these:

• https://pypi.org/project/pywebarchive
• https://github.com/robrohan/WebArchiveExtractor (GUI, but might use its logic)
• https://ss64.com/mac/textutil.html (https://apple.stackexchange.com/a/187242/314010)

Alternatives considered

Using Chrome instead of Safari.

[gy-mate]

This might not be needed as .webarchives include the HTML file.