Flume NG refactoring

To solve certain known issues and limitations, Flume requires a refactoring of some core classes and systems. This bug is a parent issue to track the development of a "Flume NG" - a poorly named, but necessary refactoring. Subtasks should be added to track individual systems and components.

The following known issues are specifically to be addressed:

• Code complexity; Flume has evolved over the last few years and has a fair amount of extraneous code.
• Core component lifecycle standardization and control code (e.g. anything that can be start()ed or stop()ed, sources, sinks).
• (Static) Configuration access throughout the code base.
• Drastic simplification of common data paths (e.g. durability as an element of the source rather than a disconnected sink).
• Heartbeat and master rearchitecture.
• Renaming packages to org.apache.flume.

This is a large and far reaching set of tasks. The intent is to perform this work in a branch as to not disrupt immediate releases or short term forthcoming releases while still allowing open development in the community.