wxGUI: always show preferences dialogs as modeless (#1132)

Fixes irrecoverable state after closing dialog on Mac.

gui/wxpython/animation/frame.py

@@ -312,7 +312,7 @@ class AnimationFrame(wx.Frame):
                 lambda: self.controller.UpdateAnimations())
             dlg.CenterOnParent()
 
-        self.dialogs['preferences'].ShowModal()
+        self.dialogs['preferences'].Show()
 
     def OnHelp(self, event):
         RunCommand('g.manual',

gui/wxpython/gmodeler/frame.py

@@ -373,7 +373,7 @@ class ModelFrame(wx.Frame):
         dlg = PreferencesDialog(parent=self, giface=self._giface)
         dlg.CenterOnParent()
 
-        dlg.ShowModal()
+        dlg.Show()
         self.canvas.Refresh()
 
     def OnHelp(self, event):

gui/wxpython/mapswipe/frame.py

@@ -751,7 +751,7 @@ class SwipeMapFrame(DoubleMapFrame):
             self._preferencesDialog = dlg
             self._preferencesDialog.CenterOnParent()
 
-        self._preferencesDialog.ShowModal()
+        self._preferencesDialog.Show()
 
     def OnCloseWindow(self, event):
         self.GetFirstMap().Clean()