add markdown/notion importer

[cloverich]

Adds an experimental Notion importer in support of #132 / #134. Once a Notion export is unzipped, use a new button in preferences screen to import the directory and referenced files:

The routine will import all markdown files, re-name and re-structure them to Chronicles format (one-level deep sub-folder for all notes, filename uuid), update note links, and import and update any referenced files

It's listed as experimental because I only tested it against my own export (~400 notes) and haven't worked through all edge cases. It uses staging tables (imports, import_notes, import_files) in a two-pass approach; the database entries can be used to understand what was imported (tracks source path and destination chronicles journal / id), but this is not exposed in the app (Its a SQLite database, easily viewed, see settings file). Once imported, the sync routine is called to synchronize the database with the new files.

Changes:

• add importer for my notion export
• add staging tables (imports, import_items, import_files)
• (refactor) re-name prior importer client to sync client
• add diff dependency for temporary hacky testing helper
• allow creating documents without indexing, to support import-then-sync approach
• types to es2020 for a misc lib function I needed

Todo:

• Add Notion import in preferences
• Re-work to import-then-sync approach
• Re-name journals and notes (remove notion id)
• Parse front matter if present
• Maintain created / updated at based on front matter or ctime / mtime
• Import tags (if in front matter as Tags)
• Import basic note links
• Import images / files and update references
• Track or log failed import items / references

Closes #134

Out of scope:

• Multi-line front matter (Support multi line YAML in front matter #256)
• More generalized markdown folder import (Import from markdown (directory) #132)
• Arbitrary front matter (hard-coded to ones I have and need; may do this though rather than discarding outright hmm)