Disassembly column should auto-scale to pane width

[hasithvm]

The disassembly/representation of each segment (the last column) should expand to fill the rest of the horizontal span of the listing view.

Steps to reproduce:

1. Load obj file
2. Observe the last column of the listing file.

Expected behavior:
The text displayed is complete

Actual behavior:
The text is truncated.

While the truncation behavior makes sense for the hex representation of each instruction/data segment, there's no practical use in truncating the source representation.