Added a DAO testing framework.

- @Dao can be used to annotate DAOs for injection, allowing them to
  either be autowired if a bean already exists or created on the fly
- @DataSet can be used to declare one or more DbUnit XML datasets to
  be used to populate data prior to running a unit test
- Revised schema to make all names (tables, columns, etc) lowercase
  - This has proven to be a best practice for achieving a database-
    agnostic system
- Added a dependency on DbUnit to allow for populating test data
- Added SchemaDtdGenerator, a JUnit test that generates an XML DTD
  describing the current database schema
- Added indexes to StormpathUserMapping's JPA configuration
- Corrected out of date logback-test.xml elements to remove Logback
  warnings output at the beginning of all tests
- Updated existing tests to use AbstractDaoTest rather than duplicating
  the various spring-test annotations on every class
- Added <dependency-management/> entries for all Spring artifacts to
  prevent mixed artifacts from being downloaded during the build
  - Fixed spring-test version to be 4.0.5 instead of 3.2.4
Add an initial user dataset and associated tests.

- Filter Flyway's schema_version table out of the schema DTD, since
  tests should never attempt to populate that table
  - Regenerated schema without this table
- Disable case-sensitive feature in DbUnit
  - This causes DbUnit to fall back on defaults drawn from the
    connected database, which makes it more robust
- Fixed wiring for the DataSetTestExecutionListener to invoke its
  initialization method, createDataSetBuilder()
- Fixed placeholder Javadocs in StormpathUserMappingRepository
Merge pull request #1 from bturner/bturner-add-dao-test-framework

Add a DAO testing framework