Add support for showing debug info on documents.

Shorten debug: prefix to just dbg:
Allow user to pass 0 or 1 as boolean values.
Use DocumentInfo instance to read from cursor in DocumentHolders.
Pass DocumentInfo instance to IconHelper to reduce zillion args.
Eliminate unnecessary State object arg from bind method.
Rename isVirtualDocument isVirtual.
Remove two unused methods from DocumentInfo.
Remove unused grid dimensions.
Address linben's ViewMode comment from previous CL.

Change-Id: I1b0c826677b69a7eaee4ee97415816aaf191121a