qt: set WWLabel text to be mouse-selectable by default

this lets user to copy-paste text in e.g. many wizard dialogs

electrum/gui/qt/util.py

@@ -92,6 +92,7 @@ class WWLabel(QLabel):
     def __init__ (self, text="", parent=None):
         QLabel.__init__(self, text, parent)
         self.setWordWrap(True)
+        self.setTextInteractionFlags(Qt.TextSelectableByMouse)
 
 
 class HelpLabel(QLabel):