mainwindow.cpp: move ensureMessageDock() member function to its own file
MessagePanel.cpp: fix column width/sort ordering bugs in populateMessages()
UI_Constructor.cpp: build custom title bar once in ensureMessageDock()
after messageDock_ exists, instead of inside the toggled handler,
ensures dock is restored visible on startup
ensureMessageDock.cpp: new member function file that handles the Message Inbox
and turns it into a Qt::Window instead of a Qt::Tool when
it is in floating mode
CMakeLists.txt: add ensureMessageDock.cpp to compile object code for the member function
