These were in some, but not all, of the existing BUILD files. They make
it easier to vendor cartographer, as Bazel complains if a BUILD file in
//third_party is missing a licenses() declaration.
This does not include cartographer_grpc, nor any of the binaries
(*_main.cc). It has been tested with Bazel 0.9.0 on Ubuntu 14.04 with
the latest (at time of writing) dazel/dazel container, by running:
```
bazel build //...
bazel test //...
```
While this is a large CL, the files under third_party are not new - they have been through internal review, and this is their open-source release. The other files come to 212 lines of code.
Rodrigo Queiro