[Travis] A basic .travis.yml config.

It builds buck and then gerrit.
Currently, it doesn't build our code at all.
[Build] Adds a BUCK file and a Module.

So that we can build the jar for the plugin.
For the moment, it does nothing, but you can run :
buck build
 buck build plugins/automerge-plugin:automerge-plugin
and it will build the plugin in
./buck-out/gen/plugins/automerge-plugin/automerge-plugin.jar
[Travis] Build the plugin in travis.

Now that the BUCK file has been added.
[Travis] Release the jar when we apply a tag.

The plugin's jar file can be stored in github releases
(https://github.com/criteo/automerge-plugin/releases) after a
travis build. Let's do that each time we apply a tag to the
github account.
[Travis] Enhance the travis.yml file.

So that we see the log file when the build fails.
Also deploy on all branches because otherwise the 'on tag'
thing does not work, and fetch tags right before deploying,
so that they are present on the slave.
[Setup] Start our plugin when gerrit starts.

So that we can listen to change events.
[Environment] Makes the README better.

So that it shows the Travis build badge, and gives more information
about what we're doing.