Updated Connected Components and Pregel Docs

Finished updating connected components to used Pregel like abstraction and created a series of tests in the AnalyticsSuite.

Adding more documentation to the Pregel API as well as additional functionality including the ability to specify the edge direction along which messages are computed.

Analytics Cleanup

Testing and Documenting VertexSetRDD

Updating analytics to reflect changes in the pregel interface and moving degree information into the edge attribute.

Refactoring IndexedRDD to VertexSetRDD.

Unit tests for Graph and GraphOps

1) This allows the index map to be optimized for Vids
2) This makes the code more readable
2) The Graph API can now return VertexSetRDDs from operations that produce results for vertices

Removing IndexedRDD changes for spark/core

Added some stub code to address the case where a vertex could occur multiple times in the vertex table or where a vertex in the edge list may not appear in the vertex table.

Moving IndexedRDD into the graphx source tree and removing dependencies in /core.

While benchmarking, we accidentally committed some unnecessary changes
to core such as adding logging. These changes make it more difficult to
merge from Spark upstream, so this commit reverts them.