Chain Spring contexts of core and web

[rwi]

Currently there are 2 separate Spring contexts, one for the core/backend beans (e.g. managers and services) and the other for the web frontend. The beans of the latter need to use a service locator to access their core bean dependencies. This should be changed so that the core Spring context becomes the parent of the web context which would allow us to use Spring DI to inject the core dependencies into the beans of the web frontend.

The technical challenging part is the web installer. It consists of a set of beans which also belongs to the web Spring context but can't be chained with the core context because the core context doesn't exist until the user completed some of the steps of the web installer.