Second set of cherry-picks from forks, all uncontentious stuff.

Fix warning - a pure expression does nothing in statement position
Fix Warning - This catches all Throwables. If this is really intended, use `case _ : Throwable` to clear this warning.
Fix deprecation warning
Upgrading aws-java-sdk library to 1.7.5
Cherry-picking my version of the upgrade to dynamodbv2. This is where my code departs from @madsmith's version (so maybe contentious).

!!BROKEN!! WIP converting to dynamodbv2
First working version passing tests
WIP BROKEN
remove commented out code block
More cherry-picks. See below for details:

Adding in Scan support
Adding BatchDeleteByID operation
Adding 'Update' operation
Make update operation return the updated version of the entity
Add support for retrieving and updating an entry using a hash + range key
Add support for querying on and creating tables with local and global secondary indexes
Clearup ambiguity  in tests for new blocking .Update
Cherry-picking the last of my fork's changes

Remove redundant ListAll operation. Scan does this perfectly well on its own
Added new feature for Delete operations to optionally return the deleted item
Adding 'overwriteExisting' flag to Save operation to allow for persisting only if PK values do not already exist in the table
Fix silly bug for with range tables and improve tests for Save operation
Cherry-picking @bkempe extensibility commit

Making Dynamo actor extensible and allowing null consumedCapacityUnits as per DynamoDB spec

Conflicts:

	src/main/scala/asyncdynamo/Dynamo.scala
	src/main/scala/asyncdynamo/TracingAmazonDynamoDB.scala
	version.sbt