Several changes:

[cbhaley]

1. Improve performance by caching all icons.
2. Use different icons instead of a check mark for notes. Sorting uses the icon.
3. In manage tags, make the edit button on the left work on all editable cells. Correct the tooltip.
4. In manage tags, put the button press shortcut descriptions into the tooltips.
5. In manage authors, add an "Edit cell" button that works with all editable cells.