Initial commit of disk_access version-2 code.

 Pulled out relevant code from the original bc_disk_access.py into this standalone script. Menu items "Open Image", "Select All", "Deselect All". "Export" and "Cancel Export" are tested to be working.
The following don't work:
- Close disk image
- Opening multiple images
- Doing "select all" will erase the past messages from the message window
- Escape characters show up in the "image info" window