Implement new feature for back button for screen tracking back with keyboard event attach

src/bitmessagekivy/main.kv

@@ -54,7 +54,16 @@ BoxLayout:
             size_hint_x: 0.1
             pos_hint: {'x': 0.8, 'y':0.4}
             on_press: app.say_exit()
-
+        ActionBar:
+            size_hint_y: 0.4
+            size_hint_x: 0.1
+            pos_hint: {'x': 0.99, 'y':0.35}
+            background_color: (0,0,0,0)
+            ActionView:
+                use_separator: True
+                ActionPrevious:
+                    with_previous: True
+                    on_release: app.set_previous_screen()
 
     ScreenManager:
         id: scr_mngr

src/bitmessagekivy/mpybit.py

@@ -19,6 +19,7 @@ from bmconfigparser import BMConfigParser
 from helper_ackPayload import genAckPayload
 from addresses import decodeAddress, addBMIfNotPresent
 from helper_sql import sqlExecute
+from kivy.core.window import Window
 
 statusIconColor = 'red'
 
@@ -38,8 +39,19 @@ class NavigateApp(App, TextInput):
         main_widget = Builder.load_file(
             os.path.join(os.path.dirname(__file__), 'main.kv'))
         self.nav_drawer = Navigator()
+        Window.bind(on_keyboard=self._key_handler)
         return main_widget
 
+    def _key_handler(self, instance, key, *args):
+        if key is 27:
+            self.set_previous_screen()
+            return True
+
+    def set_previous_screen(self):
+        if self.root.ids.scr_mngr.current != 'inbox':
+            self.root.ids.scr_mngr.transition.direction = 'left'
+            self.root.ids.scr_mngr.current = self.root.ids.scr_mngr.previous()
+
     def getCurrentAccountData(self, text):
         """Get Current Address Account Data."""
         state.association = text