Fix payment system balance integration and add calendar functionality

- Implement automated payment tracking with Django signals
- Fix duplicate transaction creation with unique referenz system
- Add calendar system with CRUD operations and event management
- Reorganize navigation menu (rename sections, move admin functions)
- Replace Geschichte editor with EasyMDE markdown editor
- Add management commands for balance reconciliation
- Create missing transactions for previously paid payments
- Ensure account balances accurately reflect all payment activity

Features added:
- Calendar entries creation and administration via menu
- Payment status tracking with automatic balance updates
- Duplicate prevention for payment transactions
- Markdown editor with live preview for Geschichte pages
- Database reconciliation tools for payment/balance sync

Bug fixes:
- Resolved IntegrityError on payment status changes
- Fixed missing account balance updates for paid payments
- Prevented duplicate balance deductions on re-saves
- Corrected menu structure and admin function placement

app/templates/stiftung/bericht_list.html

@@ -24,7 +24,7 @@
                 </div>
                 <div class="card-body">
                     <p class="text-muted mb-4">
-                        Generieren Sie detaillierte Jahresberichte mit allen wichtigen Informationen zu Personen, 
+                        Generieren Sie detaillierte Jahresberichte mit allen wichtigen Informationen zu Destinatären, 
                         Förderungen und Ländereien.
                     </p>
                     
@@ -83,8 +83,8 @@
                             <div class="card bg-primary text-white">
                                 <div class="card-body text-center">
                                     <i class="fas fa-users fa-2x mb-2"></i>
-                                    <h5 class="card-title">Personen</h5>
-                                    <h3 class="card-text">{{ total_persons|default:"0" }}</h3>
+                                    <h5 class="card-title">Destinatäre</h5>
+                                    <h3 class="card-text">{{ total_destinataere|default:"0" }}</h3>
                                 </div>
                             </div>
                         </div>
@@ -129,8 +129,8 @@
                     <div class="mt-4">
                         <h6 class="text-primary">Schnellzugriff:</h6>
                         <div class="d-grid gap-2">
-                            <a href="{% url 'stiftung:person_list' %}" class="btn btn-outline-primary">
-                                <i class="fas fa-users me-2"></i>Alle Personen anzeigen
+                            <a href="{% url 'stiftung:destinataer_list' %}" class="btn btn-outline-primary">
+                                <i class="fas fa-users me-2"></i>Alle Destinatäre anzeigen
                             </a>
                             <a href="{% url 'stiftung:foerderung_list' %}" class="btn btn-outline-success">
                                 <i class="fas fa-gift me-2"></i>Alle Förderungen anzeigen