container: introduce per-instance default options

In order to be able to set default options for common operations on a container,
introduce a default options object per operation that can be overwritten from the outside.

Together with #60 this resolves #57, because you can now do:

docker.run(..., function (...) {
  ...
}).on('container', function (container) {
  container.defaultOptions.start.Binds = ["/tmp:/tmp:rw"];
});
Merge pull request #61 from srijs/feature/container-default-options

container: introduce per-instance default options