This commit upgrades to MongoDB 3. Dependency management has been added
for the new and preferred mongodb-driver artifact. The starter has
been updated to use this new artifact rather than monogo-java-driver.
Dependency management for mongo-java-driver has been retained to avoid
causing problems for people who have declared the dependency explicitly.
The auto-configuration for Embedded Mongo has also been updated to
use 3.2.2 by default.

Closes gh-3011