Travel offers are cached to S3.

Just in case the feed breaks again.
Removed hacky logging
Adding metrics to the Travel Offers cacher.
Fixed typos.
Moved the TravelOffersCacheAgent to admin

For great singularity
Added TravelOffersCacheJob to Admin Tasklist
Renamed test
Merge remote-tracking branch 'origin/master' into persistTravelFeed

Conflicts:
	common/test/common/GuardianConfigurationTest.scala
Merge pull request #4988 from guardian/persistTravelFeed

Persist travel feed