Add VCS recording for atlantis-trunk svn checkout

[douglatornell]

Implementation will likely be almost entirely in SalishSeaCast/NEMO-Cmd, but capturing notes from issue #1 here for reference.

[douglatornell]

I did a little more research on the VCS recording with svn issue and found that, without having to authenticate to the server, svn info provides a bunch of useful stuff including:

• repo URL
• last changed rev
• last changed authored
• last changed date What's missing compared to what we can get from git are the list of files that were touched in the most recent commit, and the commit message. I'm fuzzy on whether svn has the git concept of commit and push to server, or if svn commit communicates directly with the server. So, I'm not sure if there is a case where svn info would show something different for changes that have been committed but not pushed (if that's even a thing).

svn diff also works without authentication, so we can capture uncommitted changes.