Bug 503818

Add the ability to initiate a new route search directly from any stop within an existing itinerary, particularly useful when delays cause missed connections.

Use Case
- User has an existing journey in kdeItinerary
- Train/bus is delayed, causing a missed connection
- User needs to quickly find alternative routes from their current/upcoming stop
- Without leaving the current itinerary view, user can plan a new route starting from any stop in their journey

Proposed Functionality
- Add "Plan Alternative from Here" context menu option for each stop in the itinerary
- When selected, open route planning with:
  - Pre-filled departure stop (from selected stop)
  - Original destination maintained
  - Current time + delay as departure time
- Show alternative routes that consider the actual delay situation

Benefits
- Quick recovery from disrupted journeys
- Reduced user stress during delays