Upgrade the aws-sdk-php-dependency to the most recent version (#495)

* Add required region and version, change credentials structure
* Remove references to NoSuchKeyException. The exception no longer exists, and the aws-sdk-php library now throws S3Exception instead.
* Add region and version property from phpunit configuration
* Update imageVariation tests to use new parameters. This introduces the region and version parameters for the image variation tests, as well as the new array structure for the credentials entry. We also re-use the clearBucket command from the main S3 tests.
* ImageVariations: Use new AWS client params layout
* Use the new aws-sdk-php version in composer.json. Bump the version up to the most recent version as of today.
* Bump composer.lock to new versions
* Add AWS region to the example phpunit.xml file
* Update docs for S3 adapter configuration
* Add note about upgrading to 3.0 for S3 adapters
* Update dependencies to fix issues after rebase
* Update ChangeLog

ChangeLog.markdown

@@ -5,6 +5,7 @@ Imbo-3.0.0
 ----------
 __N/A__
 
+* #495: Upgrade aws-sdk-php-dependency to new major: `^3.19` (Mats Lindh)
 * #449: Removed support for XML (Christer Edvartsen)
 * #440: Added configuration option to redirect clients hitting the index page (Christer Edvartsen)
 * #408: Moved the metadata cache event listener to a separate project: https://github.com/imbo/imbo-metadata-cache (Christer Edvartsen)

composer.json

@@ -31,7 +31,7 @@
     "mongodb/mongodb": "^1.0",
     "guzzlehttp/psr7": "^1.3",
     "doctrine/dbal": "^2.5",
-    "aws/aws-sdk-php": "^2.8"
+    "aws/aws-sdk-php": "^3.19"
   },
   "require-dev": {
     "mikey179/vfsStream": "^1.5.0",