Beta 0.5

Unit combat is now fully functional!

CHANGES TO CONQUEST.JAVA
Added method unitBattle(). Handles comparison of unit powers and calls
the killUnit() method to the appropriate unit/s after comparison. Calls
disableUnit() from ConquestMap class.
Added checkUnitsKilled() method. Ensures appropriate buttons are not
enabled if the corresponding unit is killed.
Added killUnit() method. Disables and kills the unit depending on its
set parameter.
Added disableUnitButtons() method.
Added enableUnitButtons() method.
Unit-related methods now call checkUnitsKilled().

CHANGES TO CONQUESTMAP.JAVA
Moved units to panel panelUnits.
Added a basic battlefield map to the panel panelMap.
Added disableUnitGridOccupied() method. Removes killed units from the
booleanGridOccupied array.
Move some functionality in disableUnit() method to
disableUnitGridOccupied() method.

CHANGES TO CONQUESTCOMBAT.JAVA
Added a check to see if the unit was killed in findEnemyUnits() method.
If unit was killed, it will not return true.