feat: pluggable profile tabs

Added ProfileTab class to represent a profile tab and made the profile
page render the tabs specified in the hook `profile_tabs`. This allows
plugging in new tabs in the profile page without makeing any changes to
the community module.

community/community/profile_tab.py

@@ -0,0 +1,38 @@
+"""
+The profile_tab module provides a pluggable way to add tabs to user
+profiles.
+
+This is achieved by specifying the profile_tabs in the hooks.
+
+    profile_tabs = [
+        'myapp.myapp.profile_tabs.SketchesTab'
+    ]
+
+When a profile page is rendered, these classes specified in the
+profile_hooks are instanciated with the user as argument and used to
+render the tabs.
+"""
+
+class ProfileTab:
+    """Base class for profile tabs.
+
+    Every subclass of ProfileTab must implement two methods:
+        - get_title()
+        - render()
+    """
+    def __init__(self, user):
+        self.user = user
+
+    def get_title(self):
+        """Returns the title of the tab.
+
+        Every subclass must implement this.
+        """
+        raise NotImplementedError()
+
+    def render(self):
+        """Renders the contents of the tab as HTML.
+
+        Every subclass must implement this.
+        """
+        raise NotImplementedError()