Added QWellArray from Qt

This class orginates from a private class used inside QColorDialog.
It is licensed under the LGPL v2.1 + GPL v3.0
Moved popup text changed handler into base class, and made "Name" translatable
Corrected pv::view::Trace header gates
Added pv::widgets::ColourPopup
Added pv::widgets::ColourButton
Integrated ColourButton into popup
Removed Name and Colour dialogs from context menu