This commit makes Spark invocation saner by using an assembly JAR to
find all of Spark's dependencies instead of adding all the JARs in
lib_managed. It also packages the examples into an assembly and uses
that as SPARK_EXAMPLES_JAR. Finally, it replaces the old "run" script
with two better-named scripts: "run-examples" for examples, and
"spark-class" for Spark internal classes (e.g. REPL, master, etc). This
is also designed to minimize the confusion people have in trying to use
"run" to run their own classes; it's not meant to do that, but now at
least if they look at it, they can modify run-examples to do a decent
job for them.

As part of this, Bagel's examples are also now properly moved to the
examples package instead of bagel.

Made StorageLevel constructor private, and added StorageLevels.create() to the Java API. Updates scala and java programming guides.

- Added a StorageLevels class for easy access to StorageLevel constants
  in Java
- Added doc comments on Function classes in Java
- Updated Accumulator and HadoopWriter docs slightly

- Edited quick start and tuning guide to simplify them a little
- Simplified top menu bar
- Made private a SparkContext constructor parameter that was left as
  public
- Various small fixes

also adding the version to the navbar so it is easy to tell which
version of Spark these docs were compiled for.

throughout the docs: SPARK_VERSION, SCALA_VERSION, and MESOS_VERSION.

To use them, e.g. use {{site.SPARK_VERSION}}.

Also removes uses of {{HOME_PATH}} which were being resolved to ""
by the templating system anyway.

- Rework/expand the nav bar with more of the docs site
- Removing parts of docs about EC2 and Mesos that differentiate between
  running 0.5 and before
    - Merged subheadings from running-on-amazon-ec2.html that are still relevant
      (i.e., "Using a newer version of Spark" and "Accessing Data in S3") into
      ec2-scripts.html and deleted running-on-amazon-ec2.html
- Added some TODO comments to a few docs
- Updated the blurb about AMP Camp
- Renamed programming-guide to spark-programming-guide
- Fixing typos/etc. in Standalone Spark doc