Execution Trace Log

Introduces an execution trace window that will keep track of the most
recent 10000 execution steps. I'm not entirely happy with the
implementation, yet.

src/test/java/com/loomcom/symon/CpuIndirectModeTest.java

@@ -2,7 +2,6 @@ package com.loomcom.symon;
 
 import com.loomcom.symon.devices.Memory;
 import com.loomcom.symon.exceptions.MemoryAccessException;
-import com.loomcom.symon.InstructionTable;
 
 import junit.framework.TestCase;