Add support for PDF reports

[ZIMkaRU]

This PR adds support for PDF reports

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Basic changes:

• the minimum required refactoring in order to be able to add support for pdf to the current csv generation flow
• adds logic to be able to generate PDF under Electronjs using the native api of Chromium https://www.electronjs.org/docs/latest/api/web-contents#contentsprinttopdfoptions

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How PDF generation works

For PDF generation uses browser emulation with printing HTML to PDF format:

• under Electronjs uses the internal api which used via the IPC (between framework child process and main electronjs process) with the newest browser emulation Chromium https://www.electronjs.org/docs/latest/api/web-contents#contentsprinttopdfoptions

Feature has the following flow:

• PUG templates which provide flexibility with inheritance and mixins
• render PUG template to HTML + inline CSS + inline fonts in base64 to have everything in one HTML string
• as IPC sends data between the main and child processes synchronously it works following:
  • in the framework writes HTML into temporary file asynchronously
  • send message via IPC with HTML file path to electron handler
  • under electron, reads HTML file (if ok removes temp file) and prints to PDF asynchronously
  • then writes PDF into temporary file asynchronously
  • send an answer message via IPC with PDF file path to the framework handler
  • if the framework can read the file it removes the temp file

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Depends on these PRs:

• Add support for PDF reports bfx-report#347
• Add support for PDF reports bfx-reports-framework#352

[ezewer]

lgtm!