Removed note about mouse wheel.

SDL 2.0 has a different handling of the mouse wheel anyway.  It doesn't
make sense to implement it now.
Removed notes about unit tests and exceptions.

We're not doing that.
Attempt to balance the default scenario.

One week's growth of creatures has about 100 HP and does approximately
20-40 damage.  I've taken some guesses at how traits should modify those
numbers.
Testing AI endgame logic.

The goal is to get the AI to win this battle as first player.
Currently, it can't see far enough ahead to move toward the enemy unit
(it just skips all its turns until a draw).
Default to the AI playing by itself.

Use aiBest for both sides.  Make sure the UnitView doesn't crash when
the AI wins the game.
Improved AI endgame performance.

The AI didn't have enough search depth to solve the endgame scenario.
Select a random element from any container type.
Increased endgame search complexity.
Choose from among several best actions.

Only if the active team is winning.  Endgame performance is still
lacking a bit.  The AI doesn't have a killer instinct to press its
advantage when winning.
Prevent AI from wasting mana on useless heals.