Show tooltip on memory cells where instructions were loaded or memory was set with vardefs

[facundoq]

On the instructions, the tooltip shows the instruction, its encoding, an explanation of how to encode, and higlights the byte selected.

On variable definitions, it shows the instruction that generated it, its type, and the value it represents coded in hexa, decimal and binary.

In both cases, a note reminds the user that this information is only available in the simulator, and that in real processors only the codes and values are stored, but not how to interpret them.