Improve performance of Bounding Box Context Menus

[dieknolle3333]

URL of deployed dev instance (used for testing):

• https://bboxcontextmenuperf.webknossos.xyz/

Steps to test:

• Go to bounding box tab within an annotation, have some bounding boxes laying around
• within the bounding box tab, left and right clicking the three dots aswell as right-clicking a bbox entry (almost) anywhere should open the context menu
• all enabled actions should be doing something and closing the context menu afterwards
• the context menu should close when clicking somewhere within the bounding box tab
• make sure the skeleton tab and the context menus there are looking good and behaving appropriately (minor change there to prevent horizontal scrollbar from showing up)

TODOs:

• right-clicking the whole bbox list entry should open the context menu (find out how to pass menu there)
• left-clicking the three dots should open the context menu
• close context menu after action
• fix gitch and horizontal scroll bar when opening context menu

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(Please delete unneeded items, merge only when none are left open)

• Updated changelog
• Updated migration guide if applicable
• Updated documentation if applicable
• Adapted wk-libs python client if relevant API parts change
• Removed dev-only changes like prints and application.conf edits
• Considered common edge cases
• Needs datastore update after deployment

[hotzenklotz]

This might fix #8058

[hotzenklotz]

LGTM. Works well. Thanks. 🚀