Implement Bazel build

TEST PLAN:
  $ bazel test gitiles-servlet/...

Run debug version:
  $ sh {path/to/src}/tools/run_bazel_dev.sh

TODO:

 * publishing maven artifacts.
 * check out Bazel's generate_workspace.
 * intellij/eclipse project generation

Change-Id: I288011ce622536ce72c59a1961f962db9fe9e761

.gitignore

diff --git a/.gitignore b/.gitignore
index 60ee4e8..d68222d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,3 +7,9 @@
 /.buckd
 /.idea
 *.iml
+*~
+/bazel-bin
+/bazel-genfiles
+/bazel-gitiles
+/bazel-out
+/bazel-testlogs