A more readable configuration for the calendar plugin.

The old type configuration
(`platypush.plugins.calendar.name.CalendarNamePlugin`) is a bit clunky.

Instead, since the type will always be a plugin, we should encourage
the use of `calendar.name` directly to identify the type.

platypush/config/config.yaml

@@ -301,11 +301,11 @@ backend.http:
 # # Installing the dependencies: pip install 'platypush[ical,google]'
 # calendar:
 #     calendars:
-#         - type: platypush.plugins.google.calendar.GoogleCalendarPlugin
-#         - type: platypush.plugins.calendar.ical.CalendarIcalPlugin
+#         - type: google.calendar
+#         - type: calendar.ical
 #           url: https://www.facebook.com/events/ical/upcoming/?uid=your_user_id&key=your_key
-#         - type: platypush.plugins.calendar.ical.CalendarIcalPlugin
-#           url: http://riemann/nextcloud/remote.php/dav/public-calendars/9JBWHR7iioM88Y4D?export
+#         - type: calendar.ical
+#           url: https://my.nextcloud.org/remote.php/dav/public-calendars/id?export
 ###
 
 ###

platypush/plugins/calendar/__init__.py

@@ -5,6 +5,7 @@ import importlib
 
 from abc import ABCMeta, abstractmethod
 
+from platypush.context import get_plugin
 from platypush.plugins import Plugin, action
 
 
@@ -32,10 +33,10 @@ class CalendarPlugin(Plugin, CalendarInterface):
 
                 calendars:
                     # Use the Google Calendar integration
-                    - type: platypush.plugins.google.calendar.GoogleCalendarPlugin
+                    - type: google.calendar
 
                     # Import the Facebook events calendar via iCal URL
-                    - type: platypush.plugins.calendar.ical.IcalCalendarPlugin
+                    - type: calendar.ical
                       url: https://www.facebook.com/ical/u.php?uid=USER_ID&key=FB_KEY
 
         """
@@ -44,17 +45,24 @@ class CalendarPlugin(Plugin, CalendarInterface):
         self.calendars = []
 
         for calendar in calendars:
-            if 'type' not in calendar:
+            cal_type = calendar.pop('type', None)
+            if cal_type is None:
                 self.logger.warning(
-                    "Invalid calendar with no type specified: {}".format(calendar)
+                    "Invalid calendar with no type specified: %s", calendar
                 )
                 continue
 
-            cal_type = calendar.pop('type')
+            try:
+                # New `calendar.name` format
+                cal_plugin = get_plugin(cal_type).__class__
+            except Exception:
+                # Legacy `platypush.plugins.calendar.name.CalendarNamePlugin` format
                 module_name = '.'.join(cal_type.split('.')[:-1])
                 class_name = cal_type.split('.')[-1]
                 module = importlib.import_module(module_name)
-            self.calendars.append(getattr(module, class_name)(**calendar))
+                cal_plugin = getattr(module, class_name)
+
+            self.calendars.append(cal_plugin(**calendar))
 
     @action
     def get_upcoming_events(self, max_results=10):
@@ -105,7 +113,9 @@ class CalendarPlugin(Plugin, CalendarInterface):
                 cal_events = calendar.get_upcoming_events().output or []
                 events.extend(cal_events)
             except Exception as e:
-                self.logger.warning('Could not retrieve events: {}'.format(str(e)))
+                self.logger.warning(
+                    'Could not retrieve events from calendar %s: %s', calendar, e
+                )
 
         events = sorted(
             events,