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

menu-structure.csv

@@ -0,0 +1,38 @@
+Menu Level,Item Name,URL Name,Icon,Description,Current Order
+1,Home,stiftung:home,fas fa-home,Main landing page,1
+1,Dashboard,stiftung:dashboard,fas fa-tachometer-alt,Statistics and overview dashboard,2
+2,Menschen & Finanzen (Dropdown),personenDropdown,fas fa-users,People and financial management,3
+3,Destinatäre Header,N/A,N/A,Section header,3.1
+3,Alle Destinatäre,stiftung:destinataer_list,fas fa-list,List all beneficiaries,3.2
+3,Neuer Destinatär,stiftung:destinataer_create,fas fa-plus,Create new beneficiary,3.3
+3,Förderungen Header,N/A,N/A,Section header,3.4
+3,Alle Förderungen,stiftung:foerderung_list,fas fa-gift,List all grants,3.5
+3,Neue Förderung,stiftung:foerderung_create,fas fa-plus,Create new grant,3.6
+3,Unterstützungen Header,N/A,N/A,Section header,3.7
+3,Alle Unterstützungen,stiftung:unterstuetzungen_all,fas fa-hand-holding-usd,List all support payments,3.8
+3,Neue Unterstützung,stiftung:unterstuetzung_create,fas fa-plus,Create new support,3.9
+3,Pächter Header,N/A,N/A,Section header,3.10
+3,Alle Pächter,stiftung:paechter_list,fas fa-user-tie,List all tenants,3.11
+2,Immobilien & Land (Dropdown),immobilienDropdown,fas fa-tree,Real estate and land management,4
+3,Ländereien Header,N/A,N/A,Section header,4.1
+3,Alle Ländereien,stiftung:land_list,fas fa-list,List all land parcels,4.2
+3,Neue Länderei,stiftung:land_create,fas fa-plus,Create new land parcel,4.3
+3,Verpachtungen Header,N/A,N/A,Section header,4.4
+3,Alle Verpachtungen,stiftung:verpachtung_list,fas fa-handshake,List all leases,4.5
+3,Neue Verpachtung,stiftung:verpachtung_create,fas fa-plus,Create new lease,4.6
+3,Abrechnungen Header,N/A,N/A,Section header,4.7
+3,Alle Abrechnungen,stiftung:land_abrechnung_list,fas fa-calculator,List all settlements,4.8
+3,Neue Abrechnung,stiftung:land_abrechnung_create,fas fa-plus,Create new settlement,4.9
+2,Verwaltung (Dropdown),verwaltungDropdown,fas fa-briefcase,Administration and documents,5
+3,Dokumente,stiftung:dokument_management,fas fa-folder-open,Document management,5.1
+3,Geschäftsführung,stiftung:geschaeftsfuehrung,fas fa-briefcase,Business management,5.2
+1,Geschichte,stiftung:geschichte_list,fas fa-book-open,Foundation history wiki,6
+1,Administration,stiftung:administration,fas fa-cogs,System administration,7
+2,User Menu (Dropdown),userDropdown,fas fa-user,User account management,8
+3,User Profile Header,N/A,N/A,Dynamic user name header,8.1
+3,Mein Profil,stiftung:user_detail,fas fa-user,View user profile,8.2
+3,2FA verwalten,stiftung:two_factor_setup,fas fa-shield-alt,Manage two-factor authentication,8.3
+3,Benutzerverwaltung,stiftung:user_management,fas fa-users,Manage users (admin only),8.4
+3,Administration,stiftung:administration,fas fa-cogs,System admin (admin only),8.5
+3,Abmelden,stiftung:logout,fas fa-sign-out-alt,Logout,8.6
+1,Anmelden,stiftung:login,fas fa-sign-in-alt,Login (unauthenticated users only),9