fix issues with widgets

TZPGcalc.py

@@ -412,7 +412,7 @@ class TZPGcalc():
 
         # TZPG part
         self.type = widgets.Dropdown(
-            options=TZPG_db.keys(),
+            options=list(TZPG_db),
             value='Custom',
             description='Type:',
             disabled=False
@@ -581,14 +581,14 @@ class TZPGcalc():
 
         tab1 = widgets.Accordion(children=[TZPGTab])
         tab1.set_title(0, 'TZPG')
-        tab1.selected_index = None
+        tab1.selected_index = 0
 
         tab2 = widgets.Accordion(children=[samTab])
         tab2.set_title(0, 'sample')
-        tab2.selected_index = None
+        tab2.selected_index = 0
 
         tab3 = widgets.Accordion(children=[detTab])
         tab3.set_title(0, 'detector')
-        tab3.selected_index = None
+        tab3.selected_index = 0
 
         self.control = VBox(children=[tab1, tab2, tab3, self.button])