Main Window raising fixes

On OSX and linux, the tray icon now raises window.

Starting a new instance should raise the window too, but it may not work
on linux (on my Ubuntu it just flashes the icon)

Fixes Bitmessage#743

src/bitmessageqt/__init__.py

@@ -841,6 +841,7 @@ class MyForm(settingsmixin.SMainWindow):
             self.show()
             self.setWindowState(
                 self.windowState() & ~QtCore.Qt.WindowMinimized | QtCore.Qt.WindowActive)
+            self.raise_()
             self.activateWindow()
 
     # pointer to the application