A lot of campaigns want to define custom factions. This allows them to
do so without us having to fill the built-in factions list with a bunch
of campaign-specific factions. It also makes custom campaigns more
portable as they don't need to also distribute the custom faction files.
This is used to provide a UI hint to guide players towards campaigns
that have been updated to work with the current version of the game.
All the campaigns we currently have were made for an unknown version of
the game, so they're all flagged as incompatible.
The version field is not the DCS Liberation version number because the
campaign format may change multiple times during development. Instead
the version number is a monotonically increasing integer that we
increment whenever a game change requires campaign updates.
