Add the `commit_hash` field to the GetInfoResponse. The `commit_hash`
field will contain the most recent commit_hash that the build was based
on. If the build had uncommitted changes, this field will contain the
most recent commit hash, suffixed by "-dirty".
The semantics of the `version` field is also updated to always contain
the most recent semantic version of the litd node, following the
semantic versioning 2.0.0 spec (http://semver.org/).
In this commit, a new Proxy service is added with a StopDaemon method.
This method can be used to stop the Litd service. This will be useful in
remote-mode itests where we want to restart Litd without also restarting
LND. It also provides a nice way of shutting down Litd in remote-mode.
A GetInfo method is also added to the service which for now just returns
the Litd version. The reason for adding this method now is so that
access to the new Proxy service can be tested in the itests withouth
actually shutting down Litd.
