Clippings for Thunderbird 6.1 beta 1

What's New:
• Improvements to Clippings Manager. On Windows, Clippings Manager now remembers its window size and position (issue #91)
• Improvements to support for multiple displays on Windows. Clippings popup windows and dialogs will now be positioned within the Thunderbird window from which they were opened, instead of always centered on the primary display (issue #97). This feature is experimental on macOS and Linux, where it is turned off by default
• New option to skip backup reminders if there were no changes to your clippings since the last backup (issue #95)
• In Clippings Manager, the Details Pane can be shown or hidden by pressing CTRL+D (Command+D on macOS)

Compatible with Thunderbird 78 and the latest beta release of version 91.