Improve tooltips on content views sort

The help on tooltips is confusing, it currently displays (see screenshots):

• Click on the column title to perform a single sort. Click again to change sort direction.
• Click on the arrow to add sorting criteria to existing ones. Click again to change sort direction.

This would be clearer if it stated:

• Click on the column title to sort the content on this column only. Click again to change sort order. Click on the arrows to use additional sorting criteria.
• Click on the arrow to add sorting criteria to existing ones. Click again to change sort order. To sort content on this column only, click on its title.