feat: migrate categories CLI action to views

Migrate categories CLI action to view pattern,
provide text and JSON view

src/hamster-cli.py

@@ -234,6 +234,9 @@ def current(self, action):
     def activities(self, facts):
         pass
 
+    def categories(self, facts):
+        pass
+
 class HamsterViewText(HamsterView):
 
     def current(self, action):
@@ -247,6 +250,10 @@ def activities(self, facts):
         for activity in facts:
             print("{}@{}".format(activity['name'], activity['category']))
 
+    def categories(self, categories):
+        for category in categories:
+            print(category['name'])
+
 class HamsterViewJSON(HamsterView):
 
     def _dump_fact(self, fact):
@@ -270,6 +277,11 @@ def activities(self, facts):
         output = [ {"name":activity['name'], "category":activity['category']}
             for activity in facts]
         print(json.dumps(output))
+
+    def categories(self, categories):
+        output = [ category['name'] for category in categories ]
+        print(json.dumps(output))
+
 class HamsterCli(object):
     """Command line interface."""
 
@@ -350,8 +362,7 @@ def activities(self, *args):
 
     def categories(self, *args):
         '''Print the names of all the categories.'''
-        for category in self.storage.get_categories():
-            print(category['name'])
+        self.view.categories(self.storage.get_categories())
 
 
     def list(self, *times):