General Cleanup

Address following items:

• package `org.apache.beam.sdk.extensions.euphoria.beam` deserves a better name. No need to have `beam` twice.
• Module `euphoria-local`should be removed.
• `README.md` is outdated
• `BeamExecutorContext` executor concept was removed and the `BeamExecutorContext` has become more something like `TranslationContext`. Rename It.
• `BeamFlow.java ` is created by `create(...)` set of methods, that is not consistent with rest of the API rename it to 'of(...)'.