Work In Progress: CPU behavior, UI changes

This is something of a "Work in Progress" checkpoint of several features
that are all half baked:

1. Allow loading of 16KB ROM files at address $C000 at run-time, not
   just at startup. See the "Load ROM..." File menu item.

2. Introduces the notion of "CPU Behaviors", so the core 6502 CPU
   implementation can match the behavior of either an early NMOS 6502, late
   NMOS 6502, or CMOS 65C02. Very little of this is actually implemented so
   far.

3. Adds a completely bogus implementation of the 6522 VIA (it
   does absolutely nothing right now).

4. Changes the address of the ACIA in the simulated system to match a
   real hardware implementation I put together.

src/main/java/com/loomcom/symon/devices/Via.java

@@ -0,0 +1,44 @@
+package com.loomcom.symon.devices;
+
+import com.loomcom.symon.exceptions.MemoryAccessException;
+import com.loomcom.symon.exceptions.MemoryRangeException;
+
+public class Via extends Device {
+    public static final int VIA_SIZE = 16;
+
+    private static final int ORB = 0;
+    private static final int ORA = 1;
+    private static final int DDRB = 2;
+    private static final int DDRA = 3;
+    private static final int T1C_L = 4;
+    private static final int T1C_H = 5;
+    private static final int T1L_L = 6;
+    private static final int T1L_H = 7;
+    private static final int T2C_L = 8;
+    private static final int T2C_H = 9;
+    private static final int SR = 10;
+    private static final int ACR = 11;
+    private static final int PCR = 12;
+    private static final int IFR = 13;
+    private static final int IER = 14;
+    private static final int ORA_H = 15;
+
+    public Via(int address) throws MemoryRangeException {
+      super(address, VIA_SIZE, "VIA");
+    }
+
+    @Override
+    public void write(int address, int data) throws MemoryAccessException {
+
+    }
+
+    @Override
+    public int read(int address) throws MemoryAccessException {
+        return 0;
+    }
+
+    @Override
+    public String toString() {
+        return null;
+    }
+}