refactor test suite

group integration tests under 'integration' package
add test suite (to group read/write operations which depends on each
other)
add ES as an embedded server instead of an externally managed dependency
move temporary ES data store into build/ folder
avoid index collision between tests
add preemptive index refresh after bulk insert

prevent stale data to occur for fast applications (such as tests) that
read, right after a bulk write
add option 'es.batch.write.refresh' to control this behaviour (default
true)
fixes #35
move unit tests into their own package to ease testing

update build.gradle to properly run unit and integration tests
use Suite instead of unit tests for integration testing
Fix bug in Cascading Hadoop sink affecting writing

A missing settings caused Cascading to replace the ES InputFormat with
a null implementation causing the data to be completely discarded
In addition a safety check was put in place along with a no-op
OutputCommitter to reduce the number of moving pieces
Handle unwrapping of writable objects before ES indexing