Add implicit algorithm methods for Graph; remove standalone PageRank

...hx/src/main/scala/org/apache/spark/graphx/Analytics.scala

...scala/org/apache/spark/graphx/algorithms/Algorithms.scala

.../apache/spark/graphx/algorithms/ConnectedComponents.scala

...n/scala/org/apache/spark/graphx/algorithms/PageRank.scala

...spark/graphx/algorithms/StronglyConnectedComponents.scala

...in/scala/org/apache/spark/graphx/algorithms/package.scala

...he/spark/graphx/algorithms/ConnectedComponentsSuite.scala

...la/org/apache/spark/graphx/algorithms/PageRankSuite.scala

.../graphx/algorithms/StronglyConnectedComponentsSuite.scala

...g/apache/spark/graphx/algorithms/TriangleCountSuite.scala