Implement initial framework of Bazel build

Implement initial framework of Bazel build

The initial implementation only builds the packages consumed by
Gerrit Code Review.

Test build and execution is not implemented.

We prefer to consume maven_jar custom rule from bazlets repository,
for the same reasons as in the Gerrit project:

* Caching artifacts across different clones and projects
* Exposing source classifiers and neverlink artifact

TEST PLAN:

  $ bazel build :all
  $ unzip -t bazel-genfiles/all.zip
  Archive: bazel-genfiles/all.zip
    testing: libjgit-archive.jar      OK
    testing: libjgit-servlet.jar      OK
    testing: libjgit.jar              OK
    testing: libjunit.jar             OK
  No errors detected in compressed data of bazel-genfiles/all.zip.

Change-Id: Ia837ce95d9829fe2515f37b7a04a71a4598672a0
Signed-off-by: David Ostrovsky <david@ostrovsky.org>
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>