Major Hadoop module refactoring

This commit reintroduces the titan-hadoop-core module last seen in
3a16ea2f48fbcd8bbe74884d982ef8a39e9535fd.  The core module compiles
against the same Hadoop 2.x version as the titan-hadoop-2 module, so
in the event of an oversight failure on our part that leaks a
bytecode-level Hadoop1/2 incompatibility into titan-hadoop-core, only
the titan-hadoop-1 module will break.

This is technically inferior to the strategy used prior to this
commit.  That approach had no titan-hadoop-core module.  The
titan-hadoop-1 and titan-hadoop-2 modules shared each used the build
helper plugin to add a common source directory to the build path, so
that they had one directory containing hadoop1/2-specific sources and
also had the common source directory.  The titan-hadoop-1 and -2
modules compiled every source file using their target Hadoop library
version.  This is nice because it precludes classfile linkage errors
at runtime, but the downside is that neither Eclipse m2e nor IDEA are
capable of comprehending this Maven configuration, rendering them
little more than red-colored text editors on the modules in question.

Contrast this with the approach in this commit, where
titan-hadoop-core is compiled against a Hadoop 2 jar, and it's on us
to keep out IncompatibleClassChange-inducing ABI incompatibilites.
This raises the possibility of runtime classfile linkage errors, but
the upshot is that both Eclipse and IDEA can understand it.

This commit makes a few other changes:

* deleted BlueprintsGraphOutputMapReduce and replaced calls to its
  static methods with equivalent static calls on
  TitanGraphOutputMapReduce

* deleted BlueprintsGraphOutputMapReduceTest; there is some test logic
  in here that would be nice to port to Titan, but replacing
  TinkerGraph with Titan without breaking/rewriting the test seemed
  nontrivial

* Shortened some config keys:
  titan.hadoop.graph.input.titan  -> titan.hadoop.input
  titan.hadoop.graph.output.titan -> titan.hadoop.output

The config changes are barely tested.  The config keys are probably
going to get tweaked again in the future to fit them into a
ConfigNamespace and/or to avoid potential collisions with other keys
in the titan.hadoop.graph.input prefix (e.g. "location").
Merge branch 'titan05' of github.com:thinkaurelius/titan into titan05