#148 load by bound

[robstoll]

the /fountains endpoint now requires sw and ne query parameter instead of city

moreover:

• fetch processing errors by bound
• require a location for byId so that we can look it up in cache
• fix TestCityBounds (TestCity BoundingBox has illegal specification #157)
• failure handling for cache populati
• send 404 in case json object is undefined (and not only log error
    and send undefined)
• catch errors and send to next middleware (uncaugth exception causes no response #155)
• removed database.service.ts
• increased REQUEST_LIMIT to 10MB as we query more fountains now
• updated Api.yaml accordingly
• updated express from 4.17.1 to 4.17.2
• update node-cache from 4.2.1 to 5.1.2

cleanup:

• use BoundingBox instead of separate minLng, minLat... as parameter
• added last_scan to FountainCollection and provide a factory function
    which set it automatically to new Date()
• fix binding in router.ts