Report global SVN build number in EwE

[markh]

it should also be possible to track the svn revision that generated a particular build, and this should probably be mentioned in multiple places. The 'about ewe' splash screen would be a good place, so users can mention it in bug reports. Also, all model outputs should include it as metadata, in case different builds produce slightly different results (this is something we've been uncomfortably aware of with Atlantis for a while, and Sharon Tickell from CSIRO also raised it in the context of EwE). In the case of EwE, judging by this conversation, it should also be included in the database somewhere.

I don't think this is much effort to implement (see ​http://svnbook.red-bean.com/en/1.4/svn.advanced.props.special.keywords.html), but I do think it's important to include in this kind of discussion.

[jeroens]

We can include this into the ​BuildBot daily build scripts which is fairly easy to implement. The global SVN revision number should be accessible from the core classes so it can be used anywhere in the code.

[jeroens]

Note that we are deliberately confusing 'build number' with 'svn revision number'. I think it is totally fine to use the SVN revision number instead of a build number which we do not have, but I just want to make the point.