Gitiles: Implement Buck driven build

Until extension system is released by Buck team [1], factor out
existing Buck building blocks as Bucklets in standalone git
repository and reuse it as Git submodule to implement Buck driven
build [2].

To build gitiles `gitiles` target is used:

  buck build gitiles

To build servlet, sources and javadoc in addition, `all` target is used:

  buck build all

that produces:

  buck-out/gen/gitiles.war
  buck-out/gen/servlet.jar
  buck-out/gen/src.jar
  buck-out/gen/javadoc.jar

To execute the tests:

  buck test --all

To generate eclipse project:

  bucklets/tools/eclipse.py

To fetch sources for all dependent libraries too:

  bucklets/tools/eclipse.py --src

To install gitiles-servlet into local Maven repository:

  buck build mvn_install

To deploy gitiles-servlet into remote Maven repository:

  buck build mvn_deploy

[1] http://stackoverflow.com/questions/16681527/buck-vs-gradle-pros-and-cons-for-android-build-systems
[2] https://gerrit.googlesource.com/bucklets

Change-Id: Ib824dac6423d69c298f9c30ed7a0c05b4d6447c0

.gitignore

diff --git a/.gitignore b/.gitignore
index 461cc3a..5c784fe 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,8 +1,5 @@
-.classpath
-.project
-.settings
-*/.classpath
-*/.project
-*/.settings
-*/target
-gitiles.config
+/.classpath
+/.project
+/.settings
+/buck-out
+/gitiles.config