Cleanup. Make real_transparency a bool.
Let Panel member fields end with an underscore.
Make Area::on_screen_ a bool.
Rename position fields to be less ambiguous.

The fields Panel::pos_x_ and Panel::pos_y_ are not the same as
Area::posx_ and Area::posy_, but they could've easily been confused.
Move TooltipCopyText to be a member of Tooltip.
Some cleanup in Taskbarname.
Move TaskbarBase to its own sources.

Reorganize Taskbarname a bit.
Make AddUrgent and DelUrgent members of Task.
Fix Task::UpdateTitle.