[SPARK-10599] [MLLIB] Lower communication for block matrix multiplication

This PR aims to decrease communication costs in BlockMatrix multiplication in two ways:
 - Simulate the multiplication on the driver, and figure out which blocks actually need to be shuffled
 - Send the block once to a partition, and join inside the partition rather than sending multiple copies to the same partition

**NOTE**: One important note is that right now, the old behavior of checking for multiple blocks with the same index is lost. This is not hard to add, but is a little more expensive than how it was.

Initial benchmarking showed promising results (look below), however I did hit some `FileNotFound` exceptions with the new implementation after the shuffle.

Size A: 1e5 x 1e5
Size B: 1e5 x 1e5
Block Sizes: 1024 x 1024
Sparsity: 0.01
Old implementation: 1m 13s
New implementation: 9s

cc avulanov Would you be interested in helping me benchmark this? I used your code from the mailing list (which you sent about 3 months ago?), and the old implementation didn't even run, but the new implementation completed in 268s in a 120 GB / 16 core cluster

Author: Burak Yavuz <brkyvz@gmail.com>

Closes #8757 from brkyvz/opt-bmm.