Add top level /config REST API

/config/server/ part is hard coded for now, but we may add more
config specific resource names later.

/config/server/capabilities retrieves the known server wide
capabilities list. The list has to be loaded dynamically from
the server to permit plugins to declare their own capabilities.

Change-Id: I83692bd021925d37659bfbc88b3e3b67b92c18c1
23 files changed