Disassembly window should take advantage of symbols if available

[uxmal]

I am looking at disassembled machine code but all the addresses are meaningless. If I have symbols, instead of “jmp 0x12345678”, I 'd rather see “jmp my_procedure+0x234” in the disassembly window.

Of course this applies not only to symbols obtained from symbol files but also symbols provided by the user, e.g. when renaming procedures.

I also want a toggle switch "Show symbolic addresses" in the disassembly code window. Reko should remember my choice as a user preference so that when I restart Reko I don't have to reselect this.