Tb 102: Back up folder tree icons for restoring in Tb 155

[RealRaven2000]

When updating to ESR115, Thunderbird will lose all folder tree icons as it doesn't store these in folder properties anymore.
I yet have to program a new mechanism for modifying the folder tree icons in THunderbird 115, but we can store this information for automatically restoring folder tree customization once the feature in ESR115 works and is implemented.

[RealRaven2000]

On startup, QuickFolders will automatically backup the tree customization data (all folder URLs and the locations of their icons) in the file quickFolders-FolderTree.json which will be stored in the profile/extensions folder. This will be only done once automatically. But the backup function can be invoke again manually via the QuickFolders debug menu - to access, click on QuickFolders tool button while holding down SHIFT, and then select Debug / Backup folder tree icons!

this will overwrite the last backup and store the latest icon configuration.

[RealRaven2000]

Tryout version:

QuickFolders-mx-5.17pre58.zip

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To test the preview versions above, download the zip file, drag the file into Thunderbird Add-ons Manager, do not extract contents or if won't install.

[RealRaven2000]

This has been implemented in 5.17.1, published yesterday on 07/08/2023