Use tabs instead of floating windows

* Directories dialog, Results window and ignore list dialog are the three dialog windows which can now be tabbed instead of previously floating.
* Menus are automatically updated depending on the type of dialog as the current tab. Menu items which do not apply to the currently displayed tab are disabled but not hidden.
* The floating windows logic is preserved in case we want to use them again later (I don't see why though)
* There are two different versions of the tab bar: the default one used in TabBarWindow class places the tabs next to the top menu to save screen real estate. The other option is to use TabWindow which uses a regular QTabWidget where the tab bar is placed right on top of the displayed window.
* There is a toggle option in the View menu to hide the tabs, the windows can still be navigated to with the View menu items.

qt/ignore_list_dialog.py

@@ -26,6 +26,7 @@ class IgnoreListDialog(QDialog):
     def __init__(self, parent, model, **kwargs):
         flags = Qt.CustomizeWindowHint | Qt.WindowTitleHint | Qt.WindowSystemMenuHint
         super().__init__(parent, flags, **kwargs)
+        self.specific_actions = frozenset()
         self._setupUi()
         self.model = model
         self.model.view = self
@@ -39,6 +40,7 @@ class IgnoreListDialog(QDialog):
         self.setWindowTitle(tr("Ignore List"))
         self.resize(540, 330)
         self.verticalLayout = QVBoxLayout(self)
+        self.verticalLayout.setContentsMargins(0, 0, 0, 0)
         self.tableView = QTableView()
         self.tableView.setEditTriggers(QAbstractItemView.NoEditTriggers)
         self.tableView.setSelectionMode(QAbstractItemView.ExtendedSelection)