[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.