Change to in-line attrib initialization
Replace BattleMap with BattleField class
Change attrib to in-line initialization
Consolidate buildUnit() logic; In-line attrib initialization
Add ENERGY_COST constant; In-line attrib initialization
Add on-demand player unit construction; Change "availableEnergy" to
"storedEnergy"
Check whether factory is destroyed before building new unit
Convert attribs to class constants
Rework drone AI so firing has higher priority than moving
Test modification of drawable resource
Render energy bars using resource images