use properties file to provide AWS credentials in scratch project

ditch the custom user home credentials provider
template credentials file is provided and real one is hidden by .gitignore
major: implement local integration tests with DynamoDB Local

- implement bash scripts to fetch, locally deploy, start, and stop DynamoDB Local
- integrate with SBT to start and stop DynamoDB Local
- use an SBT settings key to switch between local and remote mode (local is default)
- general reorganization of the build file
- extract code from scratch project to use as the common code for integration tests
- write an initial integration test using ScalaTest
Merge pull request #11 from pellucidanalytics/topic/dynamodb-local

Integration testing of DynamoDB mapper