Implemented adjusters' preview exclusion as described in #6 on
http://wiki.fluidproject.org/display/fluid/%28C4A%29+Preference+Editor+adjuster+mockups+for+iteration+2
Put tooltips on top of everything.
OK, indicator should be above tooltips...
This change was needed in order to solve a bug where the bottom hidden
panels where visible when the header text was more than one row.