feat: Locations: CRUD

[resah]

This issue belongs to the feature "Multiple locations": Since many offices consist of multiple floors or even different locations, it should be possible to create location with their dedicated floor plan.

---

CRUD for locations

• Properties: name (long), name (short), image, description
• Upload an image for the floorplan for the location

Backend

Endpoints:

• GET /api/locations - list all locations
• POST /api/locations - add new location
• GET /api/locations/:id - get location by ID
• PUT /api/locations/:id - update a location
• DELETE /api/locations/:id - delete a location, if no markers exist

Frontend

• Show default location