Synchronizes Wanikani Review Cache

Use the menu in the wanikani dashboard to access the script features.
A new entry at "Scripts > Settings > Sync Review Cache" will open a dialog.
1. export cache as JSON into file or clipboard on machine/browser A.
2. import cache as JSON/clipboard on machine/browser B.
3. Choose "import" to preserve data and prevent double entries.
4. Choose "overwrite" to restore backups and discard present entries.