UtBS: Make the final fight harder

Increase hp and damage of all units unique to the fight, and make the
amounts scale with difficulty level.
UtBS: Provide a partial path between enemy keeps

Should slightly encourage them to fight each other and reduces the
amount of sand slightly, making interference/attacking the keeps
somewhat harder.
UtBS: Increase difficulty of scenarios 1 and 3

Slightly fewer units in scenario 1 on hard
Deep One has more hp/attacks depending on difficulty
Less income available to player on hard in scenarios 1 and 2 to
decrease gold available in scenario 3
Added a define to make it easier to make Garak killable in scenario 3
UtBS: Make assassin appear in scenario 5

Event name was improperly identifying variable names.
UtBS: Clear a variable not used later