Merge branch 'subgraph-reuses-view' into HEAD
Create VertexPlacement on demand in VTableReplicated
Rename VTableReplicated -> ReplicatedVertexView
Revert "Create VertexPlacement on demand in VTableReplicated"

This reverts commit 32f957f3317bd62768b415da0c0cd9114f59782c.

Conflicts:
	graph/src/main/scala/org/apache/spark/graph/impl/GraphImpl.scala
	graph/src/main/scala/org/apache/spark/graph/impl/ReplicatedVertexView.scala
Merge pull request #121 from ankurdave/more-simplify

Simplify GraphImpl internals further
Adding partition level mapEdges and mapTriplets. This is necessary to support computation with random number generation.
slightly more efficient map operation