Not very usable while cfg is generating

The periodic refreshes the CFG generation performs render the interface largely unusable. Here's what I've found so far that resets every few seconds:

- Functions view column sorting
- Graph disassembly panning
- The linear disassembly is blank and throws this error on refresh:

```
File "/home/audrey/angr/angr-management/angrmanagement/ui/widgets/qunknown_block.py", line 65, in _init_widgets
self._bytes_text.append(line)
AttributeError: 'QUnknownBlock' object has no attribute '_bytes_text'
```