Use QRect instead of manually handling terminal margins

Instead of keeping track of constants and +1 -1, use a QRect to handle
the terminal margins.  There is no GUI for this currently and the
margins are hard-coded to what they are now.  Code to center the
terminal is also include (w/o GUI).

This patch comes from review 109891 w/ a few changes from me.
Thanks to Mariusz Glebocki mglb@arccos-1.net

src/ViewManager.cpp

@@ -819,6 +819,10 @@ void ViewManager::applyProfileToView(TerminalDisplay* view , const Profile::Ptr
     else if (middleClickPasteMode == Enum::PasteFromClipboard)
         view->setMiddleClickPasteMode(Enum::PasteFromClipboard);
 
+    // margin/center - these are hard-fixed ATM
+    view->setMargin(1);
+    view->setCenterContents(false);
+
     // cursor shape
     int cursorShape = profile->property<int>(Profile::CursorShape);