Uniquely identify build version

[Chordian]

@micheldebree wrote the following in a workspace task:

The macOS build automatically sets the version number of the .app bundle and the dmg image to <date>.<svn revision>.

For example 20200829.342

This way the exact same source version can be retrieved for any binary, which helps dealing with bug reports.

[Now that we have migrated to] GitHub, the SVN commit can be replaced with the commit hash. Of course this needs an automatic building proces that does this for us.

We can out this version in the title screen so we can ask people to identify which exact build they have an issue with.

[Chordian]

This is a task migrated from workstreams in Slack.

[micheldebree]

This is done for macOS and linux; the distributed artifacts and the introscreen all have the same format. eg 2020-10-21.e32a922