Add pluralizing macro filter to templating engine

- Only some plural edits are included here - some are locked behind commits coming soon™️
- Also made index template statistics variables read better
- Fixed spelling error in CSRF Error template rendering (hadn't hit the page yet)

app.py

@@ -58,7 +58,7 @@ def create_app():
 
     @app.errorhandler(CSRFError)
     def handle_csrf_error(e):
-        return render_template('errprs/csrf.html', reason=e.description), 400
+        return render_template('errors/csrf.html', reason=e.description), 400
 
     @app.before_request
     def update_last_seen():
@@ -68,6 +68,13 @@ def create_app():
             db.session.add(current_user)
             db.session.commit()
 
+    @app.template_filter('pluralize')
+    def pluralize(number, singular='', plural='s'):
+        if number == 1:
+            return singular
+        else:
+            return plural
+
     @app.context_processor
     def inject():
         return dict(now=datetime.utcnow)