Import units from Civ3 BIQ files

[QuintillusCFC]

Now that we're importing the real unit prototypes, a logical next step is importing units that are pre-placed on the map, the UNIT units in a BIQ file.

This would add a new section to ImportCiv3.cs. Use Unit.cs in the BiqSections folder of the QueryCiv3 project as the source object. Note that there is a different Unit.cs in the SavSections part of that project that will be used for a subsequent improvement for SAV files.

Other notes:

• I believe we might have code so that units will automatically pick up their graphics, but am not 100% sure about that. @maxpetul is the expert on that area.
• We don't yet have behavior for all unit attributes, e.g. airplanes. It is not expected that all scenarios' units will work in a sensible way, or even at all, after this. This is just getting them showing up on the map.
• It probably makes sense to assign the first player's units (after the barbarians) to the human player, until we get a nation-chooser implemented.

For the time being I'm not adding this to Carthage, but I'm writing it up as a relatively near-term item for scenario support. Still, that could be quite some ways down the road as I think items such as buildings, technology, and tile improvements would add more value sooner.