Use AWS ProfileCredentialsProvider on Dev machines.

Dev machines will now pickup credentials from ~/.aws/credentials

See http://blogs.aws.amazon.com/security/post/Tx3D6U6WSFGOK2H/A-New-and-Standardized-Way-to-Manage-Credentials-in-the-AWS-SDKs

At the same time you can now run most of the stack without any keys at all on a dev machine.
Merge branch 'master' of github.com:guardian/frontend into aws-credentials

Conflicts:
	common/app/model/diagnostics/CloudWatch.scala
	facia-press/app/frontpress/FrontPressCron.scala
Merge branch 'master' of github.com:guardian/frontend into aws-credentials
Merge pull request #5428 from guardian/aws-credentials

Use AWS ProfileCredentialsProvider on Dev machines.