feat: improve presentation of saved gestures table

[eglitise]

This PR has a few improvements to the Saved Gestures tab:

• Limit the table height to the Inspector window height
  • Now, if the user has many gestures, only the table contents will be scrolled, rather than the entire gestures tab
  • It is no longer necessary to scroll to the bottom of the list in order to access the add/upload buttons
  • Table header is now sticky
• Visualise the gesture over screenshot on table row mouseover, rather than on click
  • This provides more immediate feedback, and also fixes a bug where the drawn gesture remained visible after deleting the gesture
• Fix issue with duplicate keys in the gesture upload errors modal
• Increase the z-index of table button tooltips (the table sticky header was hiding them)
  • This fix was also applied to the saved capability sets table buttons