sbt: add newly required inter-module dependencies
util: update to new way of settings mgmt, general cleanup
testkit: upgrade to new spray-utils
http: smaller improvements and cleanup
httpx: upgrade to latest spray-utils and spray-http
io: upgrade
can: upgrade
caching: add explicit ExecutionContext to test (upgrade to latest spray-utils)
routing: upgrade
servlet: upgrade
client: remove obsolete structures, upgrade to latest http, utils, etc.
examples: upgrade
site: upgrade
docs: reestablish compilability (update yet to be done)