Clarify jQuery UI dependencies

[fago]

Drupal has split up jQuery UI such that you have to specify which parts of it you need to load. Also, you can make custom builds of it just containing the packages you need.

Consequently, it would be good to know which one are exactly required. It works with trial and error, but documenting them would be obviously better.

Also, clarifying on the relationship to 1.9 in the docs would help. I.e. it's only required for the tooltips or entity previews.